ACM certificate using API Gateway, can't call backend django API

Hi there,

Basically, our team tried to enable https accessibility using ACM.
Our original architecture is web server(EC2 + nginx) -> was server(django).
As far as I know, we put API Gateway before them to enable https, resulting in our architecture to be API Gateway -> web server(EC2 + nginx) -> was server(django).
By the way, we're using a SSL certificate associated with our domain name.

The problem is, we can access to the first page of our website(https://example.com).
However, when we try to login on that page, which uses a backend API in django server, the page doesn't proceed at all, and this works when we try it with a http address.

Has it something to do with nginx configuration or ACM service?
Anyone's help would be appreciated a lot.