So everything was working fine, until yesterday all of a sudden i've started getting this error:

Access to XMLHttpRequest at <URL_FOR_BACKEND> from origin '<URL_OF_FRONTEND>' has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present on the requested resource.

 

After a LOT of investigating, i finally arrived to an error in the backend which told me that our company license had expired.
We'll take care of the outdated license, but just it would have saved me a lot of hours of debugging CORS and not understanding what is the problem if the error there would be simply about the outdated license. Just an idea for the future <3