Connection to server at "127.0.0.1", port 5432 failed: Connection refused

FastAPI container fails to connect to PostgreSQL.
However, the PostgreSQL container is running well and accessible.
I don't know why this problem is happening.
Here is gist link of Dockerfile, docker-compose.yaml and log when docker-compose is run. https://gist.github.com/sunwoo1524/9f75b4d3fd295c9829705e23a3b8094d