Tell me more about the billing service: what was stored, how did you interact with the contractor?

In the billing service, we stored information about user transactions, balances, tariffs, and payment history. The data was stored in a relational database with a normalized schema to ensure integrity and quick access.

Interaction with the contractor was built through an API with a clearly described specification. We used RESTful services with authentication and request validation. The following practices were applied for integration:

• Joint planning of the API and agreement on contracts.
• Using mock services for integration testing.
• Regular meetings to discuss changes and issues.
• Logging and monitoring requests for quick error detection.

Example of interaction: when a payment was received, the contractor sent a POST request with transaction details, the service validated the data, updated the balance, and returned the operation status.