As long as it’s not a self signed cert! Then you should be good.
But it could be a SSL problem depending on what ciphers you have enabled on your server.
You’ll need to log the “failed to fetch” error out further and see what the actual issue is. It might be the toJSON that is failing and being logged as a Failed to fetch not enough of your code is here to understand what might be going on.
It’s not likely to be a CORS issue as it works on “Desktop” whoch wil apply the same CORS rules and limitations.