My firebase hosted custom domain suddenly started giving me NET::ERR_CERT_AUTHORITY_INVALID error. My assumption is this is due to a failed certificate renewal. Inspecting the invalid cert, I see it's named "testexp".
Could someone help me get a valid certificate renewal?
As @linkp was alluding, the domain registration of foreignfield.com with Network Solutions expired two days ago. That will most likely need to be renewed before a certificate for foreignfield.com can be acquired. You might be able to satisfy a DNS-01 challenge to acquire a certificate if you somehow still have control of the DNS zone for foreignfield.com, but I doubt it.
All joking aside , I concur with @Osiris's conclusions. Unless some restoration of DNS configuration is needed due to domain registration expiry, acquiring a cert should now be straightforward.
I don't see any Let's Encrypt cert issued for that domain for almost 4 years.
All recent certs were issued by Google Trust Services.
If that cert doesn't renew you'd probably be better off at a Firebase support forum. They would be more familiar with that system configuration than we would.