As a Software Engineer at Nexi Digital, you are at the heart of the European PayTech landscape. This role is critical to maintaining the high-availability infrastructure that processes millions of card transactions daily. You will be tasked with building, scaling, and securing complex financial systems that serve both merchants and consumers across diverse geographical markets. The work is inherently high-stakes and technically demanding. You will contribute to a product ecosystem that spans payment gateways, digital wallets, and merchant services. Whether you are working on backend transaction processing or full-stack integrations, your code directly influences the reliability and security of digital commerce. We look for engineers who are not only technically proficient but also deeply curious about the lifecycle of a digital payment. ##### Tip Given the scale of Nexi Digital, emphasize your experience with high-concurrency systems and your ability to maintain clean, scalable code under pressure.
Initial Screening
reportedThe process begins with an initial contact to assess basic qualifications and fit.
What to demonstrate
- The process begins with an initial contact to assess basic qualifications and fit
- Depth in Payment Systems Domain (Card Transactions)
How to prepare
- Be able to walk your CV end to end in two minutes, and say why this company specifically.
- Have your salary expectations, notice period and location constraints ready, and ask for the rest of the loop in writing.
Technical Assessment
reportedCandidates undergo deeper technical evaluations, which may involve multiple stakeholders.
What to demonstrate
- Candidates undergo deeper technical evaluations, which may involve multiple stakeholders
- Depth in Payment Systems Domain (Card Transactions)
How to prepare
- Answer aloud and timed: Have you worked with payment processing APIs or handled sensitive financial data before?
- Answer aloud and timed: Can you explain how you ensure data consistency in a distributed system?
Team Integration Evaluation
reportedAssessment of the candidate's ability to integrate into specific team structures.
What to demonstrate
- Assessment of the candidate's ability to integrate into specific team structures
- Depth in Payment Systems Domain (Card Transactions)
How to prepare
- Answer aloud and timed: Describe your experience with the specific tech stack requested in the job description.
- Answer aloud and timed: Tell me about your biggest professional achievement to date.
Final Selection
reportedThe process culminates in a final decision regarding the candidate's application.
What to demonstrate
- The process culminates in a final decision regarding the candidate's application
- Depth in Payment Systems Domain (Card Transactions)
How to prepare
- Answer aloud and timed: Describe a time you had to handle a conflict within your development team.
- Answer aloud and timed: How do you manage your time when faced with competing project deadlines?
PracHub editorial advice for the preparation topics above.
Research the Product Portfolio
Nexi Digital operates many products; knowing which one your target team manages will give you a major advantage.
Prepare for Ambiguity
Some interviews involve business case studies where there is no single right answer; focus on your logical reasoning and the trade-offs you consider.
Clarify Expectations
Don't be afraid to ask about the number of remaining rounds or the composition of the interview panel at the start of each call.
Be Ready for Behavioral Questions
Use the STAR method (Situation, Task, Action, Result) to structure your answers to behavioral questions effectively.
Choose a category, try a prompt, then open its approach, worked solution or follow-up when you need it.
How would you approach a situation where a core service begins failing in production?
How would you approach a situation where a core service begins failing in production?
Approach
- Restate the input: its shape, its size, and what is guaranteed about it.
- Name the brute-force solution and its complexity before improving on it.
- Choose the data structure from the access pattern, not from familiarity.
- State the target complexity and say which constraint rules the naive version out.
Follow-up
- How does this change if the input no longer fits in memory?
- What is the worst case, and how likely is it on real data?
You are tasked with launching a new product feature with a limited budget; how do you prioritize your developm
You are tasked with launching a new product feature with a limited budget; how do you prioritize your development efforts?
Approach
- Restate the input: its shape, its size, and what is guaranteed about it.
- Name the brute-force solution and its complexity before improving on it.
- Choose the data structure from the access pattern, not from familiarity.
- State the target complexity and say which constraint rules the naive version out.
Follow-up
- How does this change if the input no longer fits in memory?
- What is the worst case, and how likely is it on real data?
If a customer reports an issue with overcharging, what steps do you take to investigate and resolve it?
If a customer reports an issue with overcharging, what steps do you take to investigate and resolve it?
Approach
- Restate the input: its shape, its size, and what is guaranteed about it.
- Name the brute-force solution and its complexity before improving on it.
- Choose the data structure from the access pattern, not from familiarity.
- State the target complexity and say which constraint rules the naive version out.
Follow-up
- How does this change if the input no longer fits in memory?
- What is the worst case, and how likely is it on real data?
Denormalise tenant onto revisions and backfill it live
resource_revision (revision_id, resource_id, version, actor_user_id, change_kind, patch, request_id, created_at) has 400M rows and no tenant column; tenant_id lives only on resource. Two reads need it: a tenant-scoped audit feed ordered by created_at DESC, and an offboarding purge. Both join back to resource today. Justify adding tenant_id to resource_revision against those two reads, name the anomaly the copy introduces and the constraint that prevents it, then give the ordered migration for a live table taking 1.2k writes/second — the lock each step takes, how the backfill is batched, and where each step stops being reversible. PostgreSQL 16.
Approach
- Justify from the access path rather than from taste. Without the column, the audit feed either scans resource_revision by created_at and discards other tenants' rows, or resolves the tenant's resource_ids first and probes with them — both proportional to the tenant's whole history rather than to one page. With (tenant_id, created_at DESC, revision_id DESC) it is a seek that stops at 50 rows, and the purge becomes a ranged delete instead of a join.
- Name the cost exactly: a second copy of a fact can disagree with the first. Make the disagreement unwritable rather than documented — add UNIQUE (resource_id, tenant_id) on resource so it can serve as a foreign-key target, then FOREIGN KEY (resource_id, tenant_id) REFERENCES resource (resource_id, tenant_id) on the revision table. A revision can then only ever carry its parent's tenant.
- Step one, expand: ALTER TABLE resource_revision ADD COLUMN tenant_id BIGINT NULL, with no default, so it is a catalogue change and no rewrite. It still needs ACCESS EXCLUSIVE for an instant, and that instant queues behind the longest open transaction on the table while every later query queues behind it — set lock_timeout to 2s and retry rather than wait.
- Step two, dual-write: deploy the writer that populates tenant_id on every new revision while reads still use the join. Reversible by redeploying the previous build, because nothing reads the column yet.
Follow-up
- The backfill is half finished and a rollback is required. What state is the table in, and what does the previous build do with a half-populated column?
- How do you verify the backfill actually finished, given rows are still being inserted while it runs?
Keep soft-deleted accounts from blocking re-registration
app_user holds user_id, tenant_id, email CITEXT, password_hash (NULL for SSO principals), email_verified_at, auth_version, status ('invited','active','suspended','deactivated'), created_at, updated_at, deleted_at. Two live accounts for one address inside a tenant must be impossible, but an address freed by a soft delete must be reusable, and the same tenant may delete and re-register it repeatedly. Write the uniqueness DDL for PostgreSQL 16, then the equivalent for MySQL 8 where partial indexes do not exist, and say what each permits once three deleted rows already hold that address.
Approach
- Start from what is actually unique: not (tenant_id, email), but (tenant_id, email) among live rows. PostgreSQL says that directly — CREATE UNIQUE INDEX app_user_live_email ON app_user (tenant_id, email) WHERE deleted_at IS NULL. A full constraint over the same two columns burns the address permanently the first time someone deletes an account.
- Keep case-insensitivity in the type or the index, never in the application: CITEXT as given, or UNIQUE (tenant_id, lower(email)) as an expression index where the extension is unavailable. A case-sensitive unique column is exactly how two accounts for one human appear.
- For MySQL 8 the predicate has to move inside the key: add a discriminator column that is a constant 0 while the row is live and is set to user_id on delete, with UNIQUE (tenant_id, email, deleted_marker). Live rows share the constant and still collide; deleted rows differ from each other and stop colliding.
- State the NULL variant and its dependency: leaving the marker NULL for deleted rows also works, because a unique index treats NULLs as distinct — true in MySQL, and true in PostgreSQL only under the default NULLS DISTINCT, which PostgreSQL 15 lets you reverse. Check the polarity against the three existing deleted rows: constant-on-live is what preserves the collision you want, and reversing it silently admits duplicate live accounts.
Follow-up
- A deleted account re-registers with the same address the next day. Do the old resource rows follow the new user_id, and how does the API keep the two principals apart?
- How do you honour an erasure request while resource_revision.actor_user_id still references this table?
How would you design a system to handle high-volume card transaction throughput?
How would you design a system to handle high-volume card transaction throughput?
Approach
- Fix the scope first: who calls this, how often, and what they do when it fails.
- Name the read and write paths separately; they rarely have the same bottleneck.
- Choose a partition key and say what query it makes expensive.
- State the consistency you need, and where you are willing to be stale.
Follow-up
- What breaks first when traffic grows ten times?
- How does this behave when that dependency is down for an hour?
What are the fundamental differences between RESTful services and event-driven architectures in a payment envi
What are the fundamental differences between RESTful services and event-driven architectures in a payment environment?
Approach
- Fix the scope first: who calls this, how often, and what they do when it fails.
- Name the read and write paths separately; they rarely have the same bottleneck.
- Choose a partition key and say what query it makes expensive.
- State the consistency you need, and where you are willing to be stale.
Follow-up
- What breaks first when traffic grows ten times?
- How does this behave when that dependency is down for an hour?
Have you worked with payment processing APIs or handled sensitive financial data before?
Have you worked with payment processing APIs or handled sensitive financial data before?
Approach
- Clarify what is being asked and what a complete answer contains.
- State your assumptions explicitly before working the problem.
- Say what you would check first and why it is the highest-information step.
- Work from the requirement backwards to the design.
Follow-up
- What assumption would you test first?
- How would you know your answer was wrong?
Can you explain how you ensure data consistency in a distributed system?
Can you explain how you ensure data consistency in a distributed system?
Approach
- Fix the scope first: who calls this, how often, and what they do when it fails.
- Name the read and write paths separately; they rarely have the same bottleneck.
- Choose a partition key and say what query it makes expensive.
- State the consistency you need, and where you are willing to be stale.
Follow-up
- What breaks first when traffic grows ten times?
- How does this behave when that dependency is down for an hour?
Listing latency scales with page size, not with filters
The tenant listing endpoint reads resource filtered by tenant_id and status, ordered by updated_at DESC, and returns each row plus the owner's display name from app_user and the actor of that resource's latest resource_revision. p99 is 55 ms at 10 rows per page and 1.4 s at 200. Database telemetry shows 401 statements per request, each under 1 ms, and nothing in the slow-query log. Diagnose the cause and give the fix, stating the statement count per request and the p99 you expect afterwards.
Approach
- Read the counters before forming a theory. 401 statements for 200 rows is one driver query plus two per row, and sub-millisecond execution with an empty slow-query log rules out a bad plan. The time is round trips, which is why it is invisible in every per-query metric and scales with rows returned rather than with filter selectivity.
- Name the two per-row statements from their normalised text: a single-row app_user lookup by user_id, and a resource_revision lookup by resource_id ordered by version DESC LIMIT 1. Confirm by dropping those two response fields and watching the statement count fall to one. That locates the calls in the serialisation layer, not the repository.
- Check that the arithmetic accounts for the whole gap. Measure one round trip to the replica in isolation; 400 trips at roughly 3 ms of network plus 0.2 ms of execution is about 1.3 s on top of a 55 ms baseline, which matches. If the multiplication had fallen short, the N+1 would only be part of the story and you would keep looking.
- Batch both lookups. Collect owner_user_ids and resource_ids from the driver query, then issue WHERE tenant_id = $1 AND user_id = ANY($2) for the users, and PostgreSQL's SELECT DISTINCT ON (resource_id) ... WHERE resource_id = ANY($2) ORDER BY resource_id, version DESC for the latest revision, which the UNIQUE (resource_id, version) index serves directly. On an engine without DISTINCT ON, use a lateral join or a row_number window. Three statements per request at any page size.
Follow-up
- The page size is capped at 200 today. What breaks first if it is raised to 2,000, and is it still this bug?
- How do you stop the next N+1 from reaching production, given that no individual query is slow and the endpoint's tests pass?
Built from the rounds and topics Nexi Digital candidates report.
Prepare, practise & reflect
One practical outcome each day. Spend longer where you need it.
0 / 7 done01Map the Nexi Digital loop
- Write out the reported sequence: Initial Screening, Technical Assessment, Team Integration Evaluation, Final Selection.
- For each round, write one sentence on what it is judging, from the description above, and mark the one you are least ready for.
Deliverable: A one-page map of the 4 reported rounds, with the weakest marked.
02Work Payment Systems Domain (Card Transactions)
- Spend the session on Payment Systems Domain (Card Transactions), which Nexi Digital candidates report being tested on.
- Write one worked example in Payment Systems Domain (Card Transactions) and time yourself on it.
Deliverable: One timed worked example in Payment Systems Domain (Card Transactions).
03Work Card Transactions Experience
- Spend the session on Card Transactions Experience, which Nexi Digital candidates report being tested on.
- Write one worked example in Card Transactions Experience and time yourself on it.
Deliverable: One timed worked example in Card Transactions Experience.
04Work Full-Stack Development
- Spend the session on Full-Stack Development, which Nexi Digital candidates report being tested on.
- Write one worked example in Full-Stack Development and time yourself on it.
Deliverable: One timed worked example in Full-Stack Development.
05Answer out loud: Technical & Domain Knowledge
- Answer aloud, timed: How would you design a system to handle high-volume card transaction throughput?
- Answer aloud, timed: What are the fundamental differences between RESTful services and event-driven architectures in a payment environment?
Deliverable: Spoken answers to 2 reported Technical & Domain Knowledge question(s), under time.
06Answer out loud: Behavioral & Cultural Fit
- Answer aloud, timed: Tell me about your biggest professional achievement to date.
- Answer aloud, timed: Describe a time you had to handle a conflict within your development team.
Deliverable: Spoken answers to 2 reported Behavioral & Cultural Fit question(s), under time.
07Answer out loud: Problem Solving & Case Studies
- Answer aloud, timed: How would you approach a situation where a core service begins failing in production?
- Answer aloud, timed: You are tasked with launching a new product feature with a limited budget; how do you prioritize your development efforts?
Deliverable: Spoken answers to 2 reported Problem Solving & Case Studies question(s), under time.
Expand any day for tasks and deliverables. Your progress is saved on this device.
Behavioural rounds judge the decision you made and what it cost.
Describe your experience with the specific tech stack requested in the job description.
Describe your experience with the specific tech stack requested in the job description.
Approach
- Pick a story where you made the decision, not one where you watched it.
- State the situation in two sentences and spend the rest on the reasoning.
- Give the blast radius: what could have broken, and what you measured.
- Name the disagreement and how you resolved it with evidence.
Follow-up
- What would you do differently if you ran that again?
- How did you know your change caused the improvement?
Tell me about your biggest professional achievement to date.
Tell me about your biggest professional achievement to date.
Approach
- Pick a story where you made the decision, not one where you watched it.
- State the situation in two sentences and spend the rest on the reasoning.
- Give the blast radius: what could have broken, and what you measured.
- Name the disagreement and how you resolved it with evidence.
Follow-up
- What would you do differently if you ran that again?
- How did you know your change caused the improvement?
Describe a time you had to handle a conflict within your development team.
Describe a time you had to handle a conflict within your development team.
Approach
- Pick a story where you made the decision, not one where you watched it.
- State the situation in two sentences and spend the rest on the reasoning.
- Give the blast radius: what could have broken, and what you measured.
- Name the disagreement and how you resolved it with evidence.
Follow-up
- What would you do differently if you ran that again?
- How did you know your change caused the improvement?
How do you manage your time when faced with competing project deadlines?
How do you manage your time when faced with competing project deadlines?
Approach
- Pick a story where you made the decision, not one where you watched it.
- State the situation in two sentences and spend the rest on the reasoning.
- Give the blast radius: what could have broken, and what you measured.
- Name the disagreement and how you resolved it with evidence.
Follow-up
- What would you do differently if you ran that again?
- How did you know your change caused the improvement?
What attracts you to the FinTech industry, and why Nexi Digital specifically?
What attracts you to the FinTech industry, and why Nexi Digital specifically?
Approach
- Pick a story where you made the decision, not one where you watched it.
- State the situation in two sentences and spend the rest on the reasoning.
- Give the blast radius: what could have broken, and what you measured.
- Name the disagreement and how you resolved it with evidence.
Follow-up
- What would you do differently if you ran that again?
- How did you know your change caused the improvement?
Describe a situation where you had to learn a new technology on the fly to solve a problem.
Describe a situation where you had to learn a new technology on the fly to solve a problem.
Approach
- Pick a story where you made the decision, not one where you watched it.
- State the situation in two sentences and spend the rest on the reasoning.
- Give the blast radius: what could have broken, and what you measured.
- Name the disagreement and how you resolved it with evidence.
Follow-up
- What would you do differently if you ran that again?
- How did you know your change caused the improvement?
- 01
Describe your experience with the specific tech stack requested in the job description.
- 02
Tell me about your biggest professional achievement to date.
- 03
Describe a time you had to handle a conflict within your development team.
- 04
How do you manage your time when faced with competing project deadlines?
How long does the process usually take?
The process duration can vary significantly, ranging from a few weeks to several months depending on the specific team and location. It is important to stay proactive and follow up with your recruiter if you haven't heard back within the expected timeframe.
Nexi Digital Software Engineer candidate reports ↗What is the most common reason for rejection?
Candidates often struggle when they lack a clear understanding of the specific department's role or when they fail to demonstrate a "team-first" attitude. Showing genuine interest in our products and clearly articulating your past contributions is essential.
Nexi Digital Software Engineer candidate reports ↗Is it a remote-first company?
Nexi Digital supports flexible working arrangements, but expectations vary by location. Please clarify the hybrid or remote policy for your specific office during the initial HR screening.
Nexi Digital Software Engineer candidate reports ↗What topics does Nexi Digital test in interviews?
Nexi Digital interviews most often cover Stakeholder Management, Business Analysis, Account Executive (Sales) Fundamentals, Payment Systems Domain (Card Transactions), and Business Case Development. The exact emphasis depends on the specific role you apply for.
Nexi Digital Software Engineer candidate reports ↗Sources & methodology 3 sources ↗
No official company page is cited. Rounds and questions come from candidate reports and PracHub editorial material; each source shows the date it was read.
- 01Nexi Digital Software Engineer candidate reports ↗
Company-reported rounds, questions and FAQ.
Candidate reports · Accessed 2026-09-22 - 02PracHub Software Engineer practice ↗
PracHub practice material, not company-reported.
PracHub page · Accessed 2026-09-22 - 03PracHub preparation framework ↗
PracHub preparation guidance.
PracHub page · Accessed 2026-09-22
Explore related engineering environments and compare the preparation focus.
Cognition Software Engineer Interview Guide
What Cognition asks Software Engineer candidates, from reported rounds and questions.
Vercel Software Engineer Interview Guide
Debugging practice for Vercel software engineer prep built on a reproduction you trust, narrowing to the smallest failing input, and changing one variable per run so the result stays attributable.
Together Ai Software Engineer Interview Guide
Failure-handling practice for Together Ai software engineer candidates: requests whose outcome a timeout leaves unknown, where a retry is safe, and deduplicating at the receiver instead of assuming exactly-once delivery.
Spotify Software Engineer Interview Guide
Timed practice for Spotify software engineer candidates who lose time to the clock: short problems taken end to end, then reviewed against a written rubric rather than a passing test run.