I’m facing an issue with Firebase Phone Authentication in my Android app. When some users attempt to verify their phone numbers, they receive the following error:

We have blocked all requests from this device due to unusual activity. Try again later.

The issue occurs even for some new users who are trying to sign up for the first time.
Based on my research, this error is typically triggered when there are too many OTP requests in a short time span. However, this is not the case, as even first-time users are experiencing it.

What could be causing this error even for some new users?