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Challenge 09 · Season 3
The Balance Check
Match posted payments to active invoices. Find what remains unpaid.
Your task
- Ignore cancelled invoices and pending payments.
- For each active invoice, add its posted payments. Match the exact
invoice_id. - Subtract that sum from
total_cents. If the result is negative, use zero. - Count invoices with a positive balance and add those balances.
Return unpaid_invoice_count and total_outstanding_cents. No posted payments means zero paid. An overpayment cannot reduce another invoice.
Reading, starter download and connection are untimed.
Start your run
One request returns your 8 invoices and 12 payments. Build the calculation yourself. There is no practice dataset in this challenge.
Your first personal data request starts your timer when the server issues your assignment. Running the starter uses the same timer and saved data.
Read the rules first. Connecting alone does not start the timer.
My assignment
Open submissionData fields and rules
Invoices: invoice_id, status (active or cancelled), total_cents.
Payments: payment_id, invoice_id, status (posted or pending), amount_cents.
Match IDs exactly, not by row position. Each payment refers to an invoice in your packet. Invoice IDs and payment IDs are unique in their own lists. Use whole cents. Do not divide by 100 or round the answers.
Every new personal production assignment has at least one unpaid invoice. An individual invoice may have a zero balance. Re-fetching returns your original data and does not reset your timer.
Use native n8n nodes and ordinary expressions. Code, Function and Function Item nodes are not allowed, including disabled or disconnected nodes. No particular node layout is required.
Build your own solution without AI assistance. A fast time alone does not prove a violation. Personal data prevents copying someone else's answers; a general workflow can still be reused.
Finish and submit
Keep your working workflow. Export a clean copy without keys, credential references, pinned data or saved execution data. On Submit, enter both whole-number answers, upload that JSON and confirm your own-work and no-AI declarations. An explanation is optional.
File ready does not mean submitted. Wait for an accepted result and saved receipt. If the response is lost, check My result before sending another final.
Challenge 09
Submit
Upload your clean native n8n export and both whole-number answers.
Outcome unconfirmed. Keep the same request until saved status resolves it. After a real reload, reconnect and check saved status; the selected file and pending body are no longer in page memory.
Private account view
My result
Saved timing and receipt. Public standings are separate.
Connect to view saved status
Saved attempts
C09 · Season 3
Leaderboard
Challenge 09 standings, ordered by competition time.
Challenge 09 standings
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Challenge FAQ
Getting started, timing, submissions and results.
Getting started
What is the Weekly Challenge?
A small n8n task for practising your own workflow reasoning. Read the brief, build a workflow and submit the requested answers with your workflow JSON. Each challenge page explains its task and participation dates.
What do I need to take part?
An n8n instance, an n8n community account and a Weekly Challenge participant key. Use the community username shown on your forum profile. Your participant key belongs to the challenge, not your n8n login.
Can I look around before connecting my account?
Yes. Read the challenge, download the starter and view public standings without connecting. Connect with your username and current participant key when you need your personal assignment, submission or saved result.
How do I get a participant key?
Choose Create account and enter your community username and email. Check your forum inbox for the key. Registration does not start your challenge timer. Keep your key private.
When can I participate?
Use the opening, closing time and timezone published on the current challenge page. A visible page or downloadable starter does not mean submissions are open. New data requests, answer checks and submissions must meet the challenge window.
Which rules apply to my challenge?
Read the brief and the fields shown on that challenge's submission form. Answer ranges, required files and explanations can differ between challenges. Earlier challenge pages and saved results retain their original rules.
Your account and key
What does connecting my account do?
It verifies your community username and participant key so the page can show your personal actions and saved status. Connecting alone does not fetch your personal data or start the timer. Never enter your n8n password in the participant key field.
Why does my account not connect?
Check your community username and use your latest participant key. Remove accidental spaces when copying them. A replaced key no longer works. If connection still fails, keep the exact error and reference ID and contact the organisers privately. Connecting does not start your timer.
How do I recover or replace my key?
Choose Recover key and use your community username and registered email. A replacement is sent to your forum inbox. Use that new key for future requests. Recovery preserves your original assignment, timing, accepted submission and points.
What if the key message does not arrive?
Check the private messages in the same community account you registered. Do not create several accounts or post your email or key publicly. Contact the organisers with your community username and the registration or recovery error, if one appeared.
Your assignment and timer
Exactly when does the timer start?
The first successful personal data issue starts your original timer. This can happen through Start challenge or by executing the starter's personal HTTP request. Reading the brief, connecting your account and importing a starter without running that request do not start it.
Why is my assignment different from someone else's?
C09 gives you eight personal invoices and twelve payments. Everyone uses the same field names and calculation. Personal values differ. Match posted payments by exact invoice_id, ignore cancelled invoices and pending payments, and clamp each invoice balance to zero. Every new production packet has at least one unpaid invoice. Re-fetching keeps your original data.
Can I fetch again, pause or restart?
Fetching again returns your saved assignment and keeps the original first-fetch time. Closing a tab, reconnecting or replacing a key does not restart or pause the clock. Keep a safe local copy of your fetched data while you build.
Exactly when does the timer finish?
The server records a time for your complete final request at its first processing step, before the account and workflow checks. That recorded final becomes your finish only if the same request is durably accepted. Processing after that timestamp is shown separately. A browser click or local clock is not the official timestamp.
What if a technical problem costs me time?
Keep the error, request ID and approximate time with timezone, then contact the organisers. Any verified correction must be explicit and auditable. Original first-fetch and accepted records stay intact; do not assume a retry, key recovery or support message has reset your time.
Building and fair play
Which nodes can I use?
Build with native n8n nodes and normal expressions. Code, Function and Function Item nodes are prohibited, including disabled or disconnected copies. Other normal native node choices, settings and editor export metadata are supported. You do not need to copy one exact node layout.
Can I use AI assistance?
No. The challenge is for practising your own reasoning and n8n skills. Do not use AI to solve the task, plan or build the submitted workflow, generate its nodes or expressions, debug the solution, calculate answers or write the explanation.
Build and explain your own work. This also applies to AI-generated workflows that you edit before submitting.
A leaderboard position is not the goal on its own. If AI does the reasoning, you miss the practice that builds the skill. Try the steps yourself and ask for a hint in the discussion if you get stuck.
Can I use the starter and n8n documentation?
Yes. The starter fetches your personal invoices and payments and splits the two lists. It contains no practice dataset, calculation or completed solution. Read the task before running it: your first personal data issuance starts your timer. Use n8n documentation to understand native nodes and build the calculation yourself.
Can I copy or share a completed solution?
Submit your own work. Do not reuse someone else's completed challenge solution or submit their answers. Keep your personal data, answers and completed workflow out of the public discussion while participation is open. Follow the organisers' sharing instructions after the challenge.
How are integrity concerns handled?
Send concerns privately to the organisers with concrete information. Fast completion alone does not establish AI use. Eligible correct submissions are accepted automatically during the season; integrity and reward review take place at season end.
Uploads, submissions and retries
What do I submit for C09?
Submit unpaid_invoice_count, total_outstanding_cents and a clean exported workflow JSON. Both answers must be whole numbers. Personal production packets have at least one unpaid invoice and a positive outstanding total. An individual invoice can still have a zero balance. Your explanation is optional, up to 2,000 characters. Confirm the own-work and no-AI declarations.
How do I prepare the workflow JSON?
Export a copy of the workflow from your n8n editor. Clear the participant key and remove passwords, credential references, pinned data and saved execution data. Keep the normal nodes, connections and settings needed to understand your solution. Upload the JSON export itself, not a screenshot, a text summary or an execution result.
Will the challenge run or publish my workflow?
No. Uploaded workflow JSON is retained as private submission evidence and is not executed by the challenge service. Submitting it does not publish it as an n8n template or a public forum post.
What should I do if a file is rejected?
Read the exact message and check that the file is a valid, clean n8n workflow JSON export within the displayed size limit. Remove any prohibited Code, Function or Function Item node, even if it is disabled or disconnected. Wait for the file to finish loading before submitting. Keep your original export while preparing a clean copy.
How do I know my submission is complete?
Submit final must return an accepted result, and My result must show its saved receipt. Selecting a file or seeing a file-ready message does not submit it. Check saved status first if the response is lost.
Why am I asked to wait before retrying?
C09 allows five incorrect mathematical answer pairs per ten minutes. Follow the delay returned by the server. File, validation, service and delivery failures do not consume this incorrect-answer allowance. Keep the same request while an outcome is unresolved.
What if the page times out or the response is lost?
Check My result or the saved request status before creating a new final submission. Keep the same request while its outcome is being reconciled. The page retains the selected file and answers during that process; avoid refreshing or closing it until you know the saved outcome.
If the result stays unknown, contact the organisers with the request ID and exact error. A browser error alone does not tell you whether the server saved the submission.
Can I replace an accepted final by submitting again?
No. A retry after acceptance returns the original accepted receipt and does not grade a replacement upload. Keep the receipt and check your saved result. Your original acceptance and timing remain the record for that challenge.
Results, ranks and seasons
Do I have to wait for someone to approve my entry?
Eligible correct submissions are accepted automatically during the season. You do not need to wait in a human workflow-review queue to appear in the standings. Season-end integrity and reward checks are separate from that acceptance.
How is the weekly leaderboard ordered?
Accepted entries are ranked by measured competition duration, from first personal data issuance to the recorded final request that is accepted. Lower durations rank higher. Exact-duration ties share rank and points. Calendar submission order and alphabetical order do not determine rank.
How many points does a Season 3 entry earn?
Rank 1 earns 15 points, ranks 2 and 3 earn 12, and later ranks earn 11. Exact-duration ties share rank and points. Rank bonuses remain provisional while participation is open because a later entrant can finish faster.
How do season totals work?
Season 3 begins with C08. Your Season 3 total adds your C08 and C09 points. Not starting C09 does not erase your C08 points. Equal totals use the published combined completion-time rule. Season 2 results, original timings and awarded points remain available separately and are not reset or carried into Season 3.
What if my saved result or rank is unavailable?
Unavailable is different from zero or unranked. Check saved status before sending a new final, keep your receipt and contact the organisers with the exact error. The service must not invent a duration or replace your original accepted result to make a ranking appear.
Does a leaderboard position confirm a reward?
No. Use the published season announcement for the reward terms. Final eligibility and integrity checks happen at season end before rewards are confirmed. Do not assume a certificate, prize or other benefit unless it has been announced.
Support and privacy
What should I include in a bug report?
Include the challenge, your community username, the action you tried, the exact error, any request or reference ID and the approximate time with timezone. For a display problem, add your browser and device. Share only screenshots that hide keys, email addresses and private answers.
Where should I ask for help?
Use the challenge's Questions and discussion link for general task wording or platform problems. Send account access, private workflow evidence and personal timing issues directly to the organisers. Do not post your participant key or full submitted solution in the public thread.
Will an outage automatically extend the deadline?
Do not assume an extension or a timing credit. The organisers investigate reports and announce any verified repair, deadline change or scoped correction. Keep the original error and request information so the incident can be checked.
What information is public?
Public standings show community usernames and published results such as rank, points and measured time. Participant keys, registered email addresses and uploaded workflow evidence are not part of the public leaderboard. Keep secrets out of anything you share yourself.
Who can help with account or data questions?
Contact the organisers privately with your community username and a description of what you need. Do not send your participant key, n8n password or unrelated personal information. Account access and data requests should not be handled in a public challenge reply.
Create your challenge account
Use your community account. Your key arrives in your forum inbox.
Do not post your email or participant key in a public reply. Reading or recovering your key does not restart a timer.
Recover your participant key
Get a replacement key without restarting your challenge.
Do not post your email or participant key in a public reply. Reading or recovering your key does not restart a timer.
Challenges
C09 is the second challenge of Season 3. Previous results stay in the same site.
Season 3 · Challenge 09
C09: The Balance Check
Match posted payments to active invoices and find the outstanding balance.
Previous seasons
Season 2 contains C04 to C07. Its original results and timing remain unchanged.
Questions and discussion
Ask for clarification or report a platform error. Keep your key and completed solution private.
C09 discussion
For a submission issue, include the exact error and request ID. Send account and private timing details to the organisers privately.
Challenge history
Original results, points and timings remain saved.
Saved results
Earlier challenge records
Earlier results
Original earlier-season records, with their recorded points and timing.
Participant standing
Public current and historical results. Private attempts stay behind your account connection.
Season 2
Welcome,
You are connected. Connecting never starts your timer.
Browse without connecting. Connect only when you need personal actions.
Connecting reads saved status and never starts the clock.