Development of an API for the CRM system of a water delivery service + integration with the accounting system

Good day.

I will develop a high-quality and user-friendly system from scratch.
Here are my developments and examples of sections of the CRM/ERP system.

Water delivery can be conveniently visualized as Projects/Tasks
https://freelancehunt.com/showcase/work/crm-erp-sistema-upravlinnya-proektami-ta-zadachami/2032567.html

Deadlines, reminders, convenient visualization
… https://freelancehunt.com/showcase/work/crm-razdel-zavdannya-vizualizatsiya/2035422.html

Warehouse, goods and services, complete accounting
https://freelancehunt.com/showcase/work/crm-erp-modul-sklad/2037650.html

Lead processing, creating Deals and connections with tasks and Clients
https://freelancehunt.com/showcase/work/razrabotka-gibkih-moduley-crm-dlya-priyoma/2026075.html

I suggest showing what I have and discussing the technical specifications.

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Good day, I am writing on behalf of the company Devoxen. We specialize in complex backend architectures, CRM/ERP systems, integration layers, and API-first solutions. We have extensive experience in building scalable systems with event-driven architecture, webhook systems, integrations of payment services, accounting systems, and external APIs.

On the technical side, we can implement a separate integration layer (API gateway / integration layer) over the CRM with a proper modular architecture, API versioning, standardized responses, logging, event queues, and a webhook system. We will also design the structure so that any new integrations (payments, accounting, inventory, SMS, Telegram, etc.) can be connected without changing the core of the CRM.

We recommend an architecture based on REST API + event-driven approach (queues like RabbitMQ/Kafka), a separate integration service layer, and a centralized logging/monitoring system. For the first accounting integration, it is advisable to choose "Vchysno" or M.E.Doc — depending on whether document flow or deep accounting synchronization is more important to you (this will be clarified after auditing the CRM and processes).

We can do this without unnecessary questions and wasting time. We also provide a guarantee and support if desired. We will be able to start working on your project immediately after the technical audit.

I suggest moving to private messages for a more detailed technical discussion.

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Pavlo, greetings!
We are the Coderfy team, experienced in developing APIs, CRM/ERP systems, and integrations with payment services, accounting, SMS, telephony, and other external systems.

Your project looks very professional, and it is critically important to first properly design the architecture of the integration layer, rather than just "add to the API." This is exactly the kind of task we regularly work on.

As the first step, we propose to conduct a technical audit of the CRM:
— architecture analysis;
— evaluation of the database and current entities;
— checking existing APIs;
… — risk assessment;
— forming the structure of the integration layer and recommendations.

After the audit, we will prepare a clear roadmap, a list of necessary accesses, and will provide an accurate estimate of timelines and costs.

Please let us know what stack the CRM is currently developed on? We did not see this in the description — it is important for assessing the scope of work and architectural solutions.

I suggest we discuss the details 👍

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Good day.

ViACore is ready to take on the development of an API for the CRM system of a water delivery service and integration with the accounting system.

We do not just offer to "add one integration," but to lay down the correct architecture:

CRM → API CRM → integration layer → external services

This will allow for future connections to payment systems, accounting, inventory management, SMS, Telegram, telephony, and other services without reworking the core CRM.
…
What we can implement:

— technical audit of the current CRM;
— design of REST API;
— API for clients, orders, products, payments, documents, and inventory;
— webhooks/callbacks for payments, documents, orders, and inventory events;
— authorization via API keys or OAuth;
— logging of requests and errors;
— Swagger/OpenAPI or Postman documentation;
— staging/test environment for safe development;
— the first working integration with the accounting system.

After the audit of the CRM, we will be able to recommend the optimal option for accounting: Vchysly, M.E.Doc, or BAS. For the first integration, I would focus on the system where the client already has established accounting and a clear API/document exchange.

We have experience in developing CRM/ERP, APIs, integrations, business automation, and production-ready architecture. As an example of the CRM direction for water delivery:
https://aquaflow.crms.demosites.viacore.group/

ViACore:
https://viacore.group/

Approximately:
— audit and architecture design: from 300 USD;
— development of API and integration layer: from 2000–3000 USD;
— first integration with the accounting system: from 700–1500 USD;
— further support and development: from 200 USD/month.

I will provide an exact estimate after reviewing the CRM, technical specifications, database structure, current business processes, and choosing the accounting system.

We are ready to familiarize ourselves with the details and propose a step-by-step implementation plan.

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Hello! This is already a serious integration/API project of enterprise CRM architecture level. I can join as a backend/API developer and help build the right integration layer without tying business logic to specific services.

I have experience with:
— REST API architecture
— CRM/ERP integrations
— webhook/callback systems
— payment integrations (LiqPay, Stripe, Fondy, etc.)
— SaaS/backend systems
— PostgreSQL/MySQL
… — scalable integration layers
— queue/event-based architectures
— API security and role systems

Here’s how I see the architecture:
CRM Core → Internal API → Integration Layer → External Providers

What I recommend:
— versioned REST API (/api/v1/)
— service layer for integrations
— event-driven webhooks
— queue system (RabbitMQ/Redis/Celery/BullMQ)
— separate integration module for accounting/payments/SMS
— centralized logging + retry mechanisms
— staging/prod isolation

What I can cover:
— audit of the current CRM
— design of API architecture
— implementation of REST API
— webhooks/callback processing
— auth/API keys/OAuth
— OpenAPI/Swagger documentation
— integration layer
— logging and monitoring
— preparing the system for scaling

Regarding accounting integration:
for the first production integration, I often recommend Vchasy or BAS — it depends on the current business processes and document flow of the CRM. After the audit, we can determine the optimal option without overloading the system.

What is needed to start:
— access to staging CRM
— technology stack
— database structure
— current architecture
— examples of entities and business flow
— existing integrations (if any)

Regarding cost:
it depends on the state of the CRM and the volume of legacy, but this is already a middle/large backend system level, so it's better to provide an estimate after a technical audit.

I can also help build a roadmap for integrations and API governance for further scaling of the CRM without technical debt.

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Hello Pavlo! We have already collaborated. I will complete your task quickly and efficiently. I will build a CRM system with API.

My portfolio: https://freelancehunt.com/ua/freelancer/romas6ka.html#portfolio
Feel free to write, I will start working today. I look forward to collaborating with you!

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hello
Stage Number of hours
Technical audit of CRM + formation of technical specifications 4
Designing API architecture + Integration Layer 8
Development of main REST API 24
Webhooks + Callback handling 8
Integration layer + first accounting integration 16
Authorization, security, logging, versioning 4
Documentation (Swagger + README) 4
… Testing, refactoring, delivery 4
Total 72 hours

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Good day!

I have significant experience in developing scalable APIs and integrations for CRM/ERP. I expertly create architecture for payment systems, BAS/M.E.Doc/Vchysno, and other services, with a focus on scalability.

Write to me, and we will discuss the details and the optimal approach to project implementation.

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Good day. I am ready to complete this project as I have extensive experience in app development.

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Hello! I have experience in commercial development for both backend and frontend parts. I have developed APIs and integrations with third-party services. I propose to develop this system using Go + VueJS + PostgreSQL + Apache Kafka. The development can be divided into parts and conducted through a safe agreement on the service. Why this stack? Because, firstly, it is a compiled language that requires fewer resources and can handle more load with less resource usage. It can also work with concurrency and is easier to write compared to JAVA. You can write less code. I have worked in two companies that developed CRMs; the first company was Chinese for project fund accounting. The second company was Swedish for auditing activities. The cost of such a project will be 4k USD.

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Hello.

What is needed here is not just "integration," but a proper integration layer around the CRM - with API, webhooks, logging, and the ability to scale the system smoothly without rewriting the core. This is exactly how it should be built.

I can conduct an audit of the CRM, design a REST API, and implement the architecture for future integrations (payments, accounting, inventory, SMS, Telegram, etc.). For the first accounting integration, I would look towards Vchysno or BAS - depending on the current business processes and the structure of the CRM.

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Hello! I have carefully studied your project and am ready to start its implementation. Let's discuss the details for the best execution.

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Good day, I would be happy to complete your project. Please message me privately, and we will discuss the details further.

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Hello!
I have reviewed your technical specifications regarding the development of an API and integration architecture for a water delivery CRM.

I have relevant experience:

- developing REST APIs;
- CRM/ERP integrations;
- SaaS/backend architecture;
- payment integrations (Stripe, LiqPay, WayForPay);
… - webhook/callback systems;
- integration layers;
- complex Django/FastAPI backend systems;
- working with accounting and document flow services.

The architecture I recommend:

CRM Core → Internal API → Integration Layer → External Services

Key idea:
integration is not embedded directly into the CRM but works through a separate layer:

- webhook manager;
- event bus;
- adapters/connectors;
- queue system;
- retry/error handling;
- logging.

This will allow:

- connecting new services without reworking the CRM;
- scaling integrations;
- avoiding chaos in business logic;
- centrally managing errors and callbacks.

Recommended stack:

Backend:
- Python + FastAPI
- PostgreSQL
- Redis + Celery
- SQLAlchemy / Django ORM (depending on the current CRM)

API:
- REST API
- OpenAPI / Swagger
- versioning
- JWT/API keys/OAuth2

Integrations:
- webhook engine
- payment adapters
- accounting adapters
- stock adapters

Infrastructure:
- Docker
- staging/production separation
- centralized logging
- monitoring

Which accounting system do I recommend for the first integration:

For the MVP, it is best to start with:

- Vchasno — simpler integration, more modern API, fewer legacy issues.
- BAS — if you already have deep business integration with BAS.
- M.E.Doc — usually more complex due to legacy/architectural limitations.

After auditing the CRM, we can determine the optimal option.

What is needed to start:

- access to staging or a copy of the CRM;
- technology stack;
- database structure;
- examples of entities;
- current integrations;
- business processes;
- API/documentation (if available);
- access to testing environments.

I am ready to conduct a technical audit of the CRM and formulate the right approach for implementing the necessary functionality.
I will be waiting for your message!

Best regards,
Andriy

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Hello. I have extensive experience with Node.js/Python. I am ready to collaborate.

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Good day
I have reviewed the technical specifications.
I have experience in developing APIs, CRM/ERP systems, webhook integrations, and payment services. I understand the task as building a scalable integration layer, rather than just "one integration."
I can assist with:
— CRM audit
— API design
— webhook/callback logic
— REST API
— Swagger/OpenAPI documentation
… — integrations with payment systems and BAS/Vchasy
— logging and security
For the first integration, I would most likely recommend BAS or Vchasy — after analyzing the CRM, I can provide a precise recommendation.
I am ready to discuss the details and propose an optimal architecture. 👍

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Hello! I have thoroughly reviewed your technical assignment. The task is complex, architectural, but absolutely understandable. I have strong experience in Backend development with Python and creating APIs for CRM/SaaS systems (specifically, I have worked with custom implementations and automations).
I will respond to your points:
1. Architecture: I propose to build the API based on Python + FastAPI. This is a modern, fast, and secure framework. Its main advantage for your project is that it automatically generates standard documentation in Swagger / OpenAPI, which will always be up-to-date when the code changes.
2. Security: I will implement it through Middleware with the generation of unique API keys (tied to roles/permissions) and the ability to revoke them instantly. All work will be conducted exclusively on a staging server with a test database.
3. Recommendation for the first integration: I strongly recommend starting with the "Vchasy" service (Vchasy.EDO / Vchasy.Cash). Unlike BAS or M.E.Doc, "Vchasy" has a modern, well-documented REST API that allows for quick automation of creating acts, invoices, or waybills without involving external narrow-profile 1C programmers on your side. This is an ideal option for a stable MVP.
4. What is needed to start: - Access to a copy of your database (or a dump);
Test server (we can deploy my VPS or yours);
Description of the logic: which specific events should initiate the sending of Webhooks;
Access to the test cabinet of "Vchasy" (or another system that you ultimately choose).
… 5. Estimated assessment:
Development of the core API, authorization system, webhooks, and documentation: ~3 weeks.
Writing the first integration (e.g., Vchasy) and full testing: ~1.5 - 2 weeks.
Estimated project budget: +-22500 UAH (depends on the initial state of your CRM architecture and the number of entities for the API).
6. Risks: The main risk is the insufficiently normalized structure of the old CRM database, which may require writing additional "workarounds" (adapters) to produce a clean JSON. The second risk: if we choose BAS, development may be delayed due to the need for parallel configuration of HTTP services on the BAS side.
Are you ready to provide a brief description of the current infrastructure of your CRM (what it is written in and what database is used), so I can create an accurate project roadmap?

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Hello, Pavlo!

Our IT company creates and improves websites that operate reliably, quickly, and solve specific business tasks for clients. We specialize in developing websites "from scratch" as well as enhancing existing solutions, increasing their performance and user experience for your users.

We have experience in:
- developing responsive and fast websites on various platforms (WordPress, OpenCart, Shopify, WIX);
- integrations with payment systems, CRM systems, external services, and internal systems;
- optimizing website performance and security;
- setting up analytics and basic SEO tools;
… - software development and automation of business processes: managing customer databases, resource accounting, automating repetitive tasks, integrations with third-party systems;

After completing the project, we provide 14 days of technical support, during which we help adapt the system to your final business processes and consult on any questions regarding the completed work. Thanks to the free support of the completed project, this allows you to be confident that the developed solution operates reliably from the moment of launch and does not require any additional adjustments.

We work in a structured and responsible manner - focused on results that align with your business goals.

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Hello.

I am a NodeJS developer. I am ready to take on the task. Write to me, and we will discuss.

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The task is clear: not just API endpoints, but an integration layer with adapters for each external service, so that the core CRM is not affected when connecting a new one.

I will conduct a technical audit of the current CRM, design a REST API + a separate integration layer with interface contracts (PHP), and prepare documentation for the endpoints and structure for the first integration with accounting.

Which accounting system is a priority for the first stage — 1C, M.E.Doc, or something else?

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