https://www.bleepingcomputer.com/news/google/recent-google-voice-outage-caused-by-expired-certificates/

In an incident report published on Friday, Google said that a Google Voice outage affecting a majority of the telephone service's users earlier this month was caused by expired TLS certificates.

This worldwide outage prevented most Google Voice users from logging into their accounts and using the service for more than four hours between February 15th and February 16th, 2021.