While building this project, I faced several technical and architectural challenges that helped me deeply understand how Web2 and Web3 systems interact.

One major challenge was designing the middleware flow of the API gateway. Initially, it was difficult to ensure that the API existence check, payment verification, and external API fetching happened in the correct order without breaking the request flow. This caused multiple errors where APIs were being called without proper payment validation. I solved this by restructuring the route pipeline and using res.locals to securely pass API data between middlewares, making the flow clean and reliable.

Another significant hurdle was handling blockchain payment verification. Even when the blockchain explorer showed successful transactions, the token balance was not updating as expected in the application. This happened due to misunderstandings around token decimals, and asynchronous transaction confirmations. I overcame this by carefully inspecting smart contract interactions, validating token transfer events, and improving the logic for transaction verification.

I also encountered bugs in the API statistics system, such as undefined variables and incorrect database updates. For example, using an undefined id variable in the stats update logic caused runtime errors. I fixed this by correctly mapping the API identifier from the middleware and adding safeguards like upsert in MongoDB to ensure stats were created and updated reliably.

Additionally, integrating external APIs introduced challenges like handling timeouts, non-200 responses, and inconsistent data formats. I addressed this by adding proper error handling, timeouts, and standardized response structures in the API gateway.

Overall, these challenges pushed me to think beyond basic coding and design a robust, scalable architecture that connects Web2 APIs with Web3 payments in a secure and efficient way.