Hi eileeny
Preface this is not my main field of expertise and if the Braze support team has been unable to resolve this, it sounds like a real pickle but here are some thoughts.
The fact you are receiving a '410 Gone' error, suggests that the resource requested has been permanently removed. A 404 error would suggest it's a temporary problem.
For example:
If there was a document at www.braze.com/coolstuff but then it was removed permanently without a redirect to a new page setup, or proper systems put in place, it could present a '410 gone' error, as that resource no longer exists permanently and the browser (or Braze / OneSignal) doesn't know what do now.
For your use case, if the address in question is the googleapis one listed in this post, it would be interesting to see if that resource has been permanently removed and that link should be going elsewhere.
It would also be great to know if you can send push from Braze regardless of OneSignal, as it might help you narrow down which platform may be causing the issue. If you can't send a push from Braze at all, it's possible that channel isn't working. If you can send one from Braze but it breaks when OneSignal is added back in, there is a chance OneSignal is the issue.
There are a lot of pieces that could impact your current issue, so you may need to investigate each one by one to find the root cause.
Be interested to hear how this goes and see what others have to say. ☺️
