I had the same issue, but thank to this PR of SEANDOUGHTY I find out that you can use rewrite in Render to replace the proxy path in build.
You can add this to your render.yaml in your web static config
routes:
- type: rewrite
source: /.redwood/functions/*
destination: https://api.raccoon.trade/*
- type: rewrite
source: /*
destination: /index.html
or go to Redirects/Rewrites in the render.com website and set config like this
Replace https://api.raccoon.trade/*
by your API url and /.redwood/functions/*
by the same configuration on apiProxyPath in your redwood.toml file.