Hangouts

Google Hangouts is reportedly closing by June 2021, if not earlier. Are you sure it’s just not gone offline early?

https://arstechnica.com/gadgets/2019/01/the-great-google-hangouts-shutdown-begins-october-2019/

https://workspaceupdates.googleblog.com/2019/01/upcoming-hangouts-service-consolidation.html

But in any case, it’s a Google app, contact Google.

You need to contact google for help with their app.

See if this helps https://support.apple.com/en-us/HT207959