How to Deploy React frontend container with backend server container in App Platform correctly

For reference my github repository containing the frontend and server code is available at https://github.com/taymcl/PristineCleanVenturesLLC

I have a frontend container and another container that starts my server.js. The server is an Express application that listens for POST requests on the api/send-email endpoint and sends it as an email using Nodemailer. It seems that my server is started successfully according to build logs on digital ocean. When I attempt to send a POST request I get a 404 error ‘Failed to load resources’. I set my HTTP request route in the server container to /api/send-email, and set the HTTP port in the server container to 5000 as it is in my code. I just am not sure what the issue as I have tried various configurations on digital ocean and changes to my code. I have a feeling the solution is very simple and I just have lack in experience with deploying on digital ocean/configuring servers, or this is just not possible using App Platform. If I can provide any other information to help let me know.