Steam StorefrontAPI returns 403 when called on server by proxy

Question

I'm getting a 403 errors when fetching data by proxy from StorefrontAPI - docs. This seems to be an authentication error, but I can't find any auth method for this API. This error occurs only when using a remote server, but on localhost all is fine, and the same sent by Postmen returns excepted data.

My proxy server is using node.js, express and http-proxy-middleware. This is an example query: https://store.steampowered.com/api/appdetails?appids=323190 (the parameter is the game id).

I have both my backend (proxy) and frontend hosted on render.com. Here is the app adres

And for the backend

Here is the repo

(Sorry for that mess in commits, I just tried some random things to fix that problem.) I expect my app correctly fetching data from the API.