fix shopify app created by shopify cli 3

I've set up my application on a separate server, and it works fine there. But, when I try to view it through Shopify, all I get is a blank page with no content. However, if I go into the Shopify admin's iframe source and open that link in a browser, my application shows up correctly with all its content.

I think the issue is related to Content Security Policy (CSP) and CORS but I'm not sure which file to add it to, as I am new to Remix.js