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You will get Fix payment systems,SEPA transfers,cards & fintech APIs (Modulr, Unlimint)
Project details
If you're working with payment providers like Modulr, Unlimint, or similar fintech APIs and something is not working as expected, I can help you fix it properly. I work on backend payment systems and transaction flows, not just API integrations.
Typical issues I solve:
• SEPA transfers failing or not updating correctly
• incorrect transaction states or missing updates
• webhook/event synchronization problems
• card creation, activation, or transaction issues
• inconsistent balance or transaction tracking
• provider/backend desynchronization
These systems are complex and most problems are related to:
• lifecycle handling
• async event processing
• reconciliation logic
• API edge cases
What I will do:
• analyze your current payment flow
• identify the root cause
• fix the issue in a stable way
• improve consistency between provider and your backend
I’ve worked with:
• Modulr APIs
• Unlimint integrations
• transaction and payment flows
• card-related backend logic
• financial data synchronization
APIs, backend systems, Laravel, Python, MySQL, webhooks, async flows
If your payment system is unstable or behaving incorrectly, I can help you debug and fix it properly.
Typical issues I solve:
• SEPA transfers failing or not updating correctly
• incorrect transaction states or missing updates
• webhook/event synchronization problems
• card creation, activation, or transaction issues
• inconsistent balance or transaction tracking
• provider/backend desynchronization
These systems are complex and most problems are related to:
• lifecycle handling
• async event processing
• reconciliation logic
• API edge cases
What I will do:
• analyze your current payment flow
• identify the root cause
• fix the issue in a stable way
• improve consistency between provider and your backend
I’ve worked with:
• Modulr APIs
• Unlimint integrations
• transaction and payment flows
• card-related backend logic
• financial data synchronization
APIs, backend systems, Laravel, Python, MySQL, webhooks, async flows
If your payment system is unstable or behaving incorrectly, I can help you debug and fix it properly.
Programming Languages
PHP, HTML & CSS, JavaScriptCoding Expertise
SecurityWhat's included
| Service Tiers |
Starter
$150
|
Standard
$400
|
Advanced
$900
|
|---|---|---|---|
| Delivery Time | 1 day | 2 days | 3 days |
Number of Revisions | 1 | 2 | 2 |
Bug Investigation | - | ||
Fix Documentation | - | - | |
Detailed Code Comments | - | - |
8 reviews
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ET
Eddy T.
Jun 28, 2026
Laravel / PHP (Lander, Quiz, Checkout, CRM)
Milo is a super hard working senior developer with great skills. He is detailed oriented and highly recommended!
DF
David F.
Jun 10, 2020
Develop React Front end
Milos is a good developer. He is very attentive and really tries to help with his knowledge.
DF
David F.
Jun 2, 2020
Front End GUI for uploading folder to AWS API Gateway
Milos went beyond his required scope and provided a fine working experience.
SP
Sunny P.
Feb 25, 2020
Reorganize logic for mails (grouping), implement and test with third parties...add new template through third parties
Milos is truly an honourable guy. This is important to say before even going into his tech skills. I have been ripped off before by Developers. Which is easy to do as Im not a Developer!
Every feature I asked Milos to add or amend, he has given me a clear and calculated opinion and every time it has worked out. If he said he can do something, he has definitely gone and done it.
Milos has been very honest and transparent every step of the way and - it would be a pleasure to work with him again.
Every feature I asked Milos to add or amend, he has given me a clear and calculated opinion and every time it has worked out. If he said he can do something, he has definitely gone and done it.
Milos has been very honest and transparent every step of the way and - it would be a pleasure to work with him again.
SP
Sunny P.
Feb 18, 2020
Php Developer to check a web monitoring app + email notifications (intermittently working)
Milos is a smart Developer who always leads with the clients' end goal in mind. He not only fixed the issues that he was hired for, he also upgraded the app.
Milos went out of his way and above and beyond his duty to see the app was working well. We had some hurdles on the way (my fault!), but Milos was very patient and still performed exceptionally well.
Already hired him for the next project :)
Milos went out of his way and above and beyond his duty to see the app was working well. We had some hurdles on the way (my fault!), but Milos was very patient and still performed exceptionally well.
Already hired him for the next project :)
About Milos
Software Architect | AI/RAG, APIs, DevOps, Security & Payments
Zrenjanin, Serbia - 12:22 am local time
My focus is on:
AI integrations (RAG pipelines, OpenAI, automation workflows)
backend APIs (Python / FastAPI / Laravel)
payment systems (Stripe, subscriptions, webhooks, transaction flows, Cards, SEPA,...)
system stabilization and production issue fixing
Recently, I’ve been building:
RAG-based systems with hybrid retrieval (Qdrant + OpenSearch)
AI automation workflows and API services
payment integrations with complex billing logic and webhook handling
backend architectures for scalable systems
diffusion-based workflows, LoRA training, and model-serving setups for practical AI use cases
I don’t approach projects as “just coding tasks.”
Most problems I work on involve:
broken flows
unreliable integrations
scaling issues
unclear architecture decisions
If something is not working as expected, I focus on finding the root cause and fixing it properly, not patching symptoms.
Typical things I help with:
fixing Stripe subscriptions, payments, and webhook issues
building or stabilizing AI / RAG backends
debugging production API issues
designing backend architecture for new or existing systems
supporting diffusion pipelines, LoRA training workflows, and related AI infrastructure
Tech stack:
Python, FastAPI, OpenAI, Qdrant, OpenSearch, Laravel, MySQL, Docker, AWS, Hugging Face Diffusers, Transformers..
If you need someone who can quickly understand your system and fix or build it without unnecessary complexity, feel free to reach out.
*** AI Automation & RAG Engineer | OpenAI, FastAPI, Vector DB, Backend Systems ***
I build production-ready backend systems for AI-powered applications.
My focus is on:
- RAG (retrieval-augmented generation)
- OpenAI integrations
- backend APIs with Python and FastAPI
- vector search and hybrid retrieval with Qdrant and OpenSearch
- AI automation workflows
I’ve worked on systems that:
- ingest and structure knowledge from multiple sources
- perform hybrid retrieval using dense and keyword search
- generate grounded responses with LLMs
- support production-level usage, not just demos
I do not build generic chatbots.
I build systems where:
- data is structured properly
- retrieval is reliable
- outputs are grounded and controlled
Typical tasks include:
- building RAG pipelines
- developing AI backend APIs
- integrating OpenAI into existing systems
- improving retrieval quality and response grounding
- designing AI workflows and backend architecture
Tech stack:
Python, FastAPI, OpenAI, Qdrant, OpenSearch, Docker
If you need a real backend for your AI product, not just a prototype, I can help.
*** Stripe & Payment Systems Engineer | Subscriptions, Webhooks, Laravel, APIs ***
I specialize in payment systems and Stripe-based integrations.
I’ve worked on:
- subscriptions and billing flows
- webhook handling and synchronization
- failed payment recovery
- transaction logic and consistency
- card-related flows and backend systems
Most issues I fix are not simple bugs, but problems like:
- duplicate or missing webhook events
- incorrect subscription states
- payment flow inconsistencies
- retry logic issues
- reconciliation problems
I approach these systems from a backend and flow perspective, not just API calls.
Typical tasks I handle:
- Fixing broken Stripe integrations
- Debugging webhook issues
- Implementing subscription systems
- Stabilizing payment flows in production
- Backend logic for billing systems
Tech:
Stripe, Laravel, APIs, MySQL, webhooks, backend systems
If your payments are not behaving as expected, I can help you identify the root cause and fix it properly.
Steps for completing your project
After purchasing the project, send requirements so Milos can start the project.
Delivery time starts when Milos receives requirements from you.
Milos works on your project following the steps below.
Revisions may occur after the delivery date.
Analyze issue, logs, and system flow
Identify root cause and validate assumptions