Snapshot API - High error rate in Google Cloud Platform console

[imixerpro]

Hi, we've noticed high error rate in Google Cloud Platform console in one of our applications which uses cloud save functionality recently. Another project which uses cloud saves looks fine at the moment. since we use the very same SDK versions and integration code we assume that the error rate (90% peak, 82% average) might be due to high DAU and that we might hit some quotas. Testing locally sometimes we see tatusCode:403 Reason:[rateLimitExceeded] message which confirms our idea. However, checking Google Cloud quotas for the project show that we aren't hitting any limit such as queries per 100s or queries per day. Moreover, Snapshot API documentation doesn't say there are any quotas.

Could you, please, let us know the way to figure out what is the reason of high error rate and if there are any quotas?