In-app purchases no longer work.

It had an application where you could buy credits. But since I updated it to make some modifications, it no longer works. The code to implement purchases using mobile IAP is the same as before, it was not modified, so the problem is not my code. Could it be due to some compilation change in the latest versions of c3?

There have been no changes to Construct's IAP plugin in the latest release cycle. The last change was in r394 back in June which updated the underlying Cordova plugin version. So if you were already using r397.2 stable and updated to r407, there have not been any changes to IAP.