Node.js API in beanstalk returns 502 for large amount of data

I have a next.js/nodejs API deployed to Beanstalk. The API is on a EC2 server and there's a ALB in between. When the data to return is large, the API returns a 502 error, indicating that something went wrong between ALB and EC2. I tried to increasee the idle timeout on the ALB from 60s to 120s but it didn't solve the issue, and anyway the 502 occurs approximately after 45s. If the data to return is not so large, the API works as expected, suggesting it is not an application problem.

Is there anything else I can check to try to solve this issue?

thanks M