Development of Backend core (Python), Telegram FSM engine, and Stripe integration

Hello!

I have extensive experience working with Python.
I am ready to complete the assigned task.

I suggest we discuss the details in private messages.

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👋 Hello,

I am offering my candidacy. I will create an isolated backend core on your stack. I work with Python, PostgreSQL, Docker.

I will implement everything, including payment gateway integration, progression, retention scheduling, etc.

💰 Estimate - 3 weeks, $1200 (payment in two stages)

I guarantee quality and meeting deadlines. I will save your nerve cells 😀
…
PS: Due to a very unpleasant situation, I stretched the deadlines of my last project too much and received a bad review.

-> I guarantee that this is not related to quality, and I am fully motivated to do everything perfectly in the next project.

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Good day
I have extensive experience in backend development and interaction with Telegram.
Write to me.

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Hello, Sergey! Excellent, well-designed task. I would be happy to develop an independent Headless core for your EdTech product. I have a Python Core certificate and a clear academic understanding of finite state machine (FSM) architecture, which will allow me to implement isolated and fault-tolerant subscription state switching logic. I fully support your Zero Trust concept: the code will be designed to check every request and operate independently of the content. I am ready to deploy the database architecture (SQL) and test the core logic in a test environment with dummy data, integrating Stripe tests. I write clean, asynchronous, and documented code. I downloaded the attached technical specifications and am ready to study the details right now. Let's discuss the nuances in private!

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Good day.
Our team has many years of experience in developing ERP, CRM, CMS, and specialized software for businesses. We create effective digital solutions that help automate processes, increase productivity, and scale companies.

We work with modern technologies — from bots and scripts to AI agents and analytical systems. We develop websites of varying complexity. In our portfolio, we have implemented ERP solutions for the hospitality industry, as well as for companies engaged in the import and sale of goods, and our own product XFitness — an ERP system specifically designed for fitness clubs.

We are ready to implement your project and offer the best solution tailored to your needs.
Our portfolio: Freelancehunt

We specialize in the following areas:
… - Development of ERP Systems
- Development of CRM Systems
- Development of Websites of any complexity
- Development of CMS Systems
- Support for Websites
- Development of OpenCart
- Support for OpenCart
- Modification of OpenCart
- Refinement of OpenCart
- Development of WordPress
- Support for WordPress
- Modification of WordPress
- Refinement of WordPress
- Development of ECommerce
- Support for ECommerce
- Modification of ECommerce
- Refinement of ECommerce
- Development of Web Applications
- Support for 1C Servers
- Support for Web Servers
- Development of mobile applications
- Data parsing
- Development of bots
- Development of AI agents

and on the following technologies:
- Python
- PHP
- Laravel
- Symfony
- Yii2
- JS
- NodeJS
- jQuery
- TypeScript
- MySQL
- HTML
- CSS
- Vue
- Nuxt.js
- React
- React Native
- C++

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I will develop with a focus on the reliability of the architecture, scalability, and strict isolation of business logic from content, which is a key requirement of this project. I understand the specifics of building high-load backend systems and the importance of correctly implementing finite state machines, asynchronous processes, task queues, and secure handling of payment events. Special attention will be paid to transactionality, idempotency, handling of concurrent scenarios, and fault tolerance. As a result, the client will receive not just a set of separate services, but a fully independent core of the EdTech product, ready for further development and integration with any interfaces. All components will be developed with the principles of Zero Trust, testing environments, and modern security requirements in mind. Additionally, high-quality unit tests will be implemented to ensure high predictability of the system and simplify further project maintenance. The architecture will be prepared for scaling, adding new FSM scenarios, expanding subscription tiers, and integrating additional interaction channels without the need to rewrite existing logic.
Work plan:
- Detailed analysis of data structure and finite state machine.
- Design of Core Backend architecture and internal services.
- Implementation of data models and asynchronous interaction with PostgreSQL and Redis.
- Development of REST API and Telegram Gateway using FastAPI and aiogram.
- Creation of Data Driven FSM with scenario loading from JSONB.
- Implementation of subscription logic and processing of Stripe Webhooks.
- Configuration of task queues and timeout mechanisms.
… - Development of user retention module and task scheduler.
- Implementation of protection mechanisms, request limits, and secure token comparison.
- Implementation of QA functionality and environment isolation.
- Preparation of Docker Compose infrastructure.
- Creation of unit tests and compliance check with Bandit requirements.
- Final testing and preparation of the system for further integration.

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Hello! I am a Python developer with 8 years of experience in building backends of varying complexity. I have worked with FastAPI, PostgreSQL, Redis, and Docker. I have also developed Telegram bots of various complexity, including subscription projects. I can implement your project in full accordance with the technical specifications.

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I have built similar systems: subscription logic with Stripe Webhooks, isolation of the business core from content, and Telegram bots using aiogram with FSM machines. Here I see three layers: the core with the domain model and subscriptions, Stripe integration with payment/cancellation event handling, and an FSM engine on top that knows nothing about content, only about user states. A question about architecture: is the subscription tied to the user at the core level, or is access to content resolved by a separate service with each request? I am ready to discuss the details and structure of the MVP.

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Good day.

I have extensive experience in Python development, working with FastAPI, PostgreSQL, Redis, and Docker. I also have experience in developing Telegram bots and implementing complex business logic.

The project specification looks clear and close to my specialization. I am particularly interested in the section with FSM, PostgreSQL, and Stripe webhooks.

I am ready to familiarize myself in detail with the full project specification, after which I will be able to clarify the timelines and cost of the work.

I would be happy to collaborate.

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Hello! Is there a plan to use an existing FSM framework, or does the state logic need to be written from scratch for your unique subscription business model?

I will clarify the deadlines and budget in personal correspondence.

1. I will implement a fully isolated headless core, where the subscription logic and data processing do not depend on the content.
2. I will deploy all development in a Zero Trust test environment, using only dummy data and test keys.
3. I will implement the finite state machine (FSM) according to your specifications, ensuring strict state validation and security.

Thank you for considering my proposal. I look forward to the opportunity to collaborate with you!

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Hello! My name is Ruslan, a Middle Backend developer with about 2.5 years of commercial experience.

Stack: Node.js / TypeScript / NestJS / Python / PostgreSQL / Redis / Docker / event-driven architecture.

Relevant experience for your project:

— Worked with subscription logic and billing, integration of payment providers
— Implemented FSM / state machine patterns in production systems
— Built isolated API cores with clear boundaries between modules
… — PostgreSQL is the main DB, I understand schemas, migrations, complex queries
— Docker, test environments, working with dummy data is standard practice

I have reviewed the description — the Zero Trust architecture and headless core with content isolation is an interesting and understandable task. I am ready to study the technical specifications in detail from the file.

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Hello. I work with Python and FastAPI. I am ready for collaboration.

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Hello!

I read the technical specifications: headless Python core — data-driven FSM (JSONB + hot-reload), strict subscription with linear progression, Stripe webhooks (signature + idempotency by event_id + raw logs for replay), pessimistic locks against race conditions, Redis timeouts, retention cron. It closely aligns with what I have already done.

The most relevant experience is concurrency and payments: on an online taxi platform, I implemented 4 SQL-level idempotency patterns that eliminated double charges and order duplicates under load (multi-node + parallel crons). This is exactly your race condition case when validating PIN + idempotency by event_id. I built idempotent processing of payment events + reconciliation + ledger (other gateways; Stripe webhooks — the same pattern).

FSM: I created a 14-state subscription finite state machine + order-FSM for the taxi; I also implemented hot-reload of worker configs without restarting the instance (= your /api/admin/reload).

Stack: Python async + FastAPI, SQLAlchemy 2.0 (async), Docker Compose, SMTP for HTML reports, pytest. I wrote async bots using aiogram 3.x on python-telegram-bot, the same model.
…
Question: is each level a separate Stripe price, or is it one rebill gate? This affects the box_licenses scheme and FSM transitions.

I will provide an estimate based on the specifications; I work on an hourly rate of approximately $25/hour. Details will be discussed in correspondence.

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Hello!

I have fully reviewed the specifications — the architecture is clear, and I have no questions about the stack.

My experience is relevant:
— I work with FastAPI, aiogram 3.x, PostgreSQL, SQLAlchemy 2.0, Redis
— I have implemented Telegram bots with multi-step scenarios and operator modes
— I have experience with queue tasks, webhook processing, and asynchronous architecture
— I have written pytest tests, with 100% coverage of critical business logic
…
Based on the specifications, I see the following stages:
1. Database architecture + migrations (users, fsm_nodes, stripe_raw_events, etc.)
2. FSM engine with data-driven logic and hot reloading
3. Stripe webhooks — idempotency, signature validation, rebill business logic
4. Redis timeouts (soft/hard), rate limiting via Token Bucket
5. Retention cron job + SMTP report
6. Docker Compose, pytest (80%+), Bandit — clean report

I will detail the plan and timelines in private.

Cost: 22,500 UAH (15 working days × 1,500 UAH).

I hope for cooperation!

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Good day! I have worked on Python bots and services with FSM logic and Stripe — I connected subscriptions via webhooks with payment status checks. A headless core, isolated from content, on a test circuit with dummy data — the architecture is clear, and the asynchronous stack on asyncpg is my main focus. I will look at the specifications in detail and verify the database structure. Please let me know right away: are we using the ready-made Stripe Billing with price/product, or are we creating our own subscription cycle on webhooks? This affects the timeline, approximately 10-12 days.

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Good day!

I am a professional developer specializing in Backend cores using Python, FSM engines for Telegram, and integrating payment systems, including Stripe. I am ready to implement an independent Headless core for your EdTech product, ensuring complete isolation of logic and strict adherence to security requirements in the testing environment (Zero Trust).

I have experience with FSM, APIs, and subscription systems. Please write to me, and we can clarify the details.

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Hello Sergey! This is Nina, the manager of the backend development team.

We have studied the detailed addition to the technical specifications. Excellent, technically mature architecture. The requirements for asyncpg, JSONB matrices, pessimistic locking, and security are fully accepted.

How Valentin will implement the key nodes of the system:
Transactionality and Progression: We will handle PIN code validation and subscription level checks through pessimistic locks SELECT ... FOR UPDATE in SQLAlchemy 2.0 Core, completely eliminating Race Condition during parallel requests.
Stripe Webhooks: We will implement strict idempotency by stripe_event_id, signature validation, and mandatory saving of raw logs in stripe_raw_events for replay analysis.

Data-Driven FSM & Timeouts: The engine on aiogram 3.x will be fully isolated and tied to parsing JSONB from fsm_nodes. We will set up the endpoint /api/admin/reload for hot reloading the matrix in memory. The logic of Soft/Hard timeouts will be implemented through Redis keys with programmatic revocation of Celery/Taskiq tasks upon response.
…
Retention & Security: We will configure the HTML report assembly based on the formula activated_at + 26 days through the scheduler. Protection will be ensured through Token Bucket in Redis, hash comparison via hmac.compare_digest(), and a hidden QA module that can be disabled in production.

Conditions and Acceptance:
Cost: 25,000 UAH (fixed through Safe).
Deadline: 14 days.

Deliverables: Clean Docker Compose, 100% validation of business logic in pytest (coverage 80%+) and a clean report from the Bandit scanner (0 vulnerabilities High/Medium).

Sergey, as a task scheduler for timeouts and retention workers, we are deploying the Taskiq + Redis bundle (it works lighter and faster in the asynchronous context of Python 3.11+) or are you strictly tied to classic Celery + RabbitMQ?

We are ready to enter the test environment and start coding!

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We have experience in creating scalable Backend systems in Python using asynchronous FSM engines for Telegram. We implement architecture with complete isolation of logic from content and ensure secure integration of Stripe for the subscription model. We guarantee adherence to Zero Trust principles during development in the testing environment. We are ready to start implementing the core of your EdTech product.

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