I've submitted a game for the Gdevelop 3d Jam that uses an API in the background. It was mainly the core of the game. Without it, the game could never be finished/experienced. Everything worked perfectly, not only on preview, but also my test builds. When I submitted to itch.io, the browser version didn't work. I knew it was that API calls were not working, but I couldn't diagnose further. The game didn't work for anyone. My advice is to take 1 day to entirely to test the in browser experience on itch.io, as it is the main source of players. We don't have many tools to find about what's going on itch.io or a debug mode AFAIK.
Viewing post in Strange behavior with the game in the Browser
I even made some decisions taking into account my friend's buggy version, however, the fact that his computer runs the normal game and mine, which is now having a problem, makes testing not enough.
Anyway, I'll get into the habit of submitting the game to itch.io more often, I also almost didn't manage to sign up for JAM because of problems I had in the last 10 minutes of the event, anyway, that's good advice, thanks .