Why am I suddenly getting the [firebase_auth/too-many-requests] error when trying to fetch SMS verification messages?

Question

I'm getting this error when trying to get sms verification message on my production app:

[firebase_auth/too-many-requests] We have blocked all requests from this device due to unusual activity. Try again later.

My app has over 70k users over the last few years and this is the only time this error started popping up for every user, the app is linked to it's firebase project and app check play integrity is on and all hashes are added to their respective places.

Any idea what could suddenly cause this?