Withdrawal and deposit system on the site with escrow

Budget: 550 USD Deadline: 13 days

Greetings! Your project requires not just code refinement, but ensuring the financial consistency of the system. I specialize in creating fault-tolerant solutions and am ready to take on the stabilization of your payment system.

Answers to your questions:

Experience with payments: I have worked with Stripe and PayPal integrations, setting up commission logic and fund distribution among participants.

Escrow: I implemented the logic of "freezing" funds in the system's balance with subsequent release after confirming the fulfillment of obligations.

Webhook retries: I use idempotent keys (Idempotency-Key) for processing repeated requests. Each webhook event is logged, and the transaction status changes atomically, which eliminates duplication during retries from Stripe/PayPal.

Protection against double charges: I use database-level transactions (Database Locks) and check unique operation identifiers before executing the charge. This eliminates race conditions even under high load.

My work plan:

Audit: I will analyze the current database architecture and order flow to identify bottlenecks in balance consistency.

Stabilization: I will implement state checks (State Machine) for the wallet to ensure that fund transfers are transparent and secure.

Escrow and Payout: I will implement correct commission calculations (8% and 6%) and a secure flow for payments to sellers.

Examples of work:
My project https://integraljobs.cz/ demonstrates the ability to work with user data and complex form logic. I am also currently developing a high-load booking system (Block 2 - CI/CD, security, working with queues).

I am building my rating on the platform, so I guarantee exceptional attention to the security of your code and adherence to deadlines. Expand

Budget: 3850 USD Deadline: 15 days

Understood, I will compress as much as possible. Here is a professional response for the client that includes the main points: experience, technical solution, and price.
🚀 Response to the payment system refinement
Hello! I have extensive experience in fintech projects and automating complex transactions (30+ cases). I understand that the main focus here is data integrity and handling edge cases.
1. Experience: Integrated Stripe (Connect/Custom), PayPal, WhiteBit. Implemented multi-wallets with payment splitting logic.
2. Escrow: Created systems with fund freezing (locked_balance) until the order_completed trigger or dispute resolution.
3. Webhooks: Used Idempotency Keys. First, I record event_id in the database, return 200 OK, and move the logic (accrual) to background queues (Redis/RabbitMQ).
4. Protection against double charges: * Database Transactions: Atomic operations (minus for one, plus for another).
* Select for Update: Locking the wallet row during the transaction to avoid Race Conditions.
* Idempotency: Unique keys for each financial operation at the API level.
🛠 Work plan:
* Audit: Checking the database architecture and commission calculations (8% and 6%).
* Stabilization: Implementing Double-entry bookkeeping (balance = sum of transactions).
* Escrow & Withdrawal: Correct logic for payments to the seller after deducting the commission.
* Tests: Writing Unit tests for all mathematical operations and rounding.
⏱ Deadline: 10–15 working days.
💰 Cost: $2,000 – $3,500 (after code analysis).
Why me: I don’t just fix the code, but create a system where every penny of commission is under control. Bonus: I will set up Sentry error monitoring for payments.
What stack is the project written in (Node.js/Python/PHP)? Ready for code analysis! Expand

Budget: 50 USD Deadline: 1 day

Hello.

I am a NodeJS developer. I have experience with Stripe integration. I am ready to take on the project. Write to me, and we will discuss.

1. Have you worked with payment systems?
Yes.

2. Have you done escrow?
Yes, I have experience with an escrow Telegram bot.

3. How do you handle webhook retries?
Check by transaction ID and save statuses in the database.

4. How do you protect against double charges?
Assign unique keys to payments, check the status before each operation. Expand

Budget: 2000 USD Deadline: 15 days

Hello,

I’m an experienced developer with a strong background in payment systems and marketplace architectures. I’ve worked on wallet infrastructures, payment integrations (including Stripe and PayPal), and have implemented escrow flows ensuring secure and reliable transactions.

I have hands-on experience handling webhook retries using idempotency keys and event validation, and I protect against double charges through transaction locking, unique request identifiers, and careful state management to prevent race conditions.

I’ve also built and stabilized systems involving balance consistency, commission logic, and withdrawal processes, always focusing on production reliability and clean, maintainable code.

I’m comfortable analyzing existing codebases, identifying weak points, and improving them without disrupting current functionality.

I’d be happy to review your system and help bring it to a stable production level.

Best regards,
Jeo Vincent Carretas Expand

Budget: 1350 USD Deadline: 15 days

Hello, mate.

Yes, I have worked extensively with payment systems and marketplace flows, including wallet logic, commission handling, webhook driven updates, and payout processes. I have also worked on escrow style flows where funds are reserved, released on completion, and kept consistent across edge cases.

My approach here is to first audit the current payment architecture and trace every state change before touching live logic. Then I would harden top up, escrow, seller release, withdrawal fees, buyer commission, and webhook handling with strict idempotency keys, transactional database updates, retry safe event processing, and locking to prevent race conditions and double charges.

For webhook retries, I process events in an idempotent way and store event IDs so repeats are ignored safely. For double charge protection, I combine idempotency keys, verified payment states, and atomic updates.

For examples of my work is exeltiqcom

Thank you. Expand

Budget: 200 USD Deadline: 3 days

Hello! Your project looks wonderful. I am ready to start working immediately and complete it at a high level.

Budget: 36 USD Deadline: 1 day

Hello. I have extensive experience in website development and payment systems. Can I see a link to the website?

Budget: 200 USD Deadline: 1 day

Hello! I am ready to complete this project and have extensive experience in developing various applications.

Budget: 25 USD Deadline: 1 day

Good day!

We are the Devoxen team, and we have extensive experience in refining payment systems and fintech solutions.

We understand that the task is not from scratch — we first conduct an analysis of the current implementation, after which we carefully stabilize the key parts: wallet logic, escrow, webhook processing, and protection against double charges, without disrupting the already functioning features.

I suggest we move to private messages for a more detailed discussion of the technical specifications, timelines, and pricing.

Budget: 1800 USD Deadline: 14 days

Hello.

This is the kind of task where the main work is not “adding payments”, but making the existing financial flow stable and safe under real conditions.

From your description, the critical part is:

correct wallet state
escrow freeze / release logic
withdrawal handling
webhook reliability
protection against duplicate operations, retries, and race conditions
all of that without breaking orders, users, and chats already tied to the current flow

I would approach this in 2 steps:

1. Analyze the current implementation first
Map payment states, transaction flow, webhook handling, balance updates, and weak points.

2. Stabilize and finalize the system
Fix/refactor the unsafe parts, then bring top-up / escrow / seller transfer / withdrawal logic to production level.

Answers to your questions:

1. Have you worked with payment systems?
Yes — especially where the important part is not only provider connection, but correct payment flow handling, retries, and transaction safety.

2. Have you done escrow?
I understand escrow logic well: funds should move through explicit states, remain frozen until the correct completion event, and only then be released or refunded according to the transaction flow.

3. How do you handle webhook retries?
Through idempotent event processing: unique event IDs, deduplication, persisted processing state, and safe retry behavior so repeated webhook delivery does not duplicate balance changes or payouts.

4. How do you protect against double charges / double operations?
Idempotency keys, atomic DB updates / transactions where needed, strict payment state transitions, locking or concurrency-safe update patterns, and separation between “payment received” and “funds applied to balance”.

5. Examples of work
I prefer to discuss implementation approach based on your current stack and codebase, because in systems like this the quality of the solution matters more than generic claims.

My recommendation is to start with a paid analysis stage, then proceed to fixes in milestones. That is the safest way for a partially implemented marketplace payment system.

Estimated budget: $1800–2600
Estimated timeline: 10–14 days
If needed, I can also split it into:

audit / plan
core fixes
payout / withdrawal / hardening

What backend stack is the current marketplace using? Expand

Budget: 650 USD Deadline: 5 days

Hello!

I looked at the task — this is exactly the type of work that interests me. Not "build from scratch," but to understand someone else's code, find weak spots, and bring the system to production level without breaking what already works.

I will respond point by point:

1. Have I worked with payment systems?
Yes. I implemented the full cycle of integrations with Stripe (PaymentIntents, Connect, payouts, refunds) and PayPal (Orders API, Webhooks). I also integrated crypto payments through Coinbase Commerce and custom on-chain transaction verification. I understand not only "how to call the API," but also why payment systems behave the way they do — especially in edge cases.

2. Have I done escrow?
Yes. I implemented hold logic: funds are frozen in the balance after payment, transferred to the seller only after deal confirmation, with automatic release after a timeout or manually. Separately — the refund mechanism in disputes. I understand that the main thing here is the consistency of state, not just "movement of money."

3. How do I handle webhook retries?
Webhooks are a separate topic. I save each incoming webhook in the database with a unique event_id until processed. Before any business logic — a check for already processed events (idempotency). Signature verification (Stripe-Signature / PayPal-Auth-Algo) is mandatory. I respond with 200 immediately, processing goes into a queue (Bull/Redis or similar). A retry storm from the provider is not scary in this case.

4. How do I protect against double charges?
Combination: idempotent keys on the payment provider side + pessimistic locks (SELECT FOR UPDATE) at the database level during balance operations + unique indexes on transactions + a state machine for orders that excludes double charges. I close race conditions at the database transaction level, not at the application level.

5. Examples of work?
I am ready to show code snippets and architectural solutions from real projects at a meeting (under NDA, so no public links). I can describe a specific case verbally or in writing.

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Regarding my approach to your project: first of all — an audit of the current code. I look at transaction states, balance logic, webhook entry points, and where race conditions may occur. Only after that — a plan for improvements with priorities, without chaotic changes.

I am ready to discuss the details. When is it convenient to call? Expand

Budget: 2500 USD Deadline: 15 days

Hello!

I am ready to connect to the improvement of your payment system and bring it to a stable production level. I understand that the task is not to develop from scratch, but to stabilize the financial logic, fix edge cases, and protect against errors.

Experience
Stripe / PayPal / crypto integrations
Wallets, transactions, balances
Escrow (hold → release → refund)
Webhook and asynchronous processes
Working with race conditions and idempotency

Implementation vision
I will start with an audit of the system:
checking transaction logic
searching for race conditions
analyzing webhook
checking balance consistency

I recommend (if not yet implemented):
switching to a ledger model (transaction journal) instead of a simple balance

Main improvements
Stabilization of the wallet
Implementation/fixing of escrow
Correct commission logic (8% / 6%)
Safe processing of webhook
Protection against double charge
Idempotency of operations
Queue and statuses of fund withdrawals

Reliability
storing event_id (anti-duplicates for webhook)
DB transactions + row locking
checking payment statuses before recording

Estimation
Timeline: 10–20 days

Answers
1. Payments? Yes (Stripe, PayPal, crypto)
2. Escrow? Yes (hold/release/refund)
3. Webhook retries? Idempotency + event_id
4. Double charge? Checks + DB transactions
5. Examples? I will send in private messages

I am ready to start with the audit and quickly get to work 🚀

Best regards, Expand