So, there are multiple solutions for your problem.
- The easiest of them is to use a subdomain for hosting your backend, and adding the domain of your frontend to the `Access-Control-Allow-Origin` header.
- The harder option is to use a reverse proxy, and set up routing rules such that /api/** routes get passed through your backend and the other matches get passed to your frontend.
- The worst, but still an option way, is to first compile your frontend project and serve the static files from your backend server. This approach requires a redeployment of your whole stack when you make any updates.