Firebase hosting does not deploy on custom domain

It will take some time, usually in the magnitude of minutes (rather than hours, and certainly not days) to start working, but looking at the "google domains setup" screenshot, I believe there is an issue with the DNS setup as the screenshot shows an incomplete configuration.

For anyone else looking to resolve this, I will write the complete steps to help resolve the issue, for Firebase and Google Domains: retrace these steps, since any one of them could be the source of the issue.

First on Firebase Hosting:

1. Click add custom domain
2. Enter the custom domain or subdomain in the provided input box (note the difference!)
3. Lastly firebase will show a screen with details of how to configure the DNS. The "quick setup" is sufficient for new sites. It will look like this:

The next step is to enter this information into the domain name provider's console, in this case Google domains.

On Google Domains console:

1. Go to DNS configuration, then "custom records" section
2. Since this is a newly registered domain, there should not be existing records, but otherwise see the blue star note above: "Remember to remove..."
3. "create new record"
4. To get this last part correctly requires paying attention to the difference in how to configure domain/subdomain, so I will present them separately to highlight the difference:

Option A) subdomain configuration e.g. www.mywebsite.com

The entry in the DNS configuration should look as follows, where the data is the IPv4 address from Firebase. Note for "host name", enter the subdomain-part only:

Option B) domain name configuration e.g. mywebsite.com

The host name entry is intentionally left blank, and data is the IPv4 obtained from Firebase.

Save the DNS changes then wait. If you return to Firebase hosting, it may say "needs setup" ... then "pending" ... while these changes are being propagated and waiting for a SSL cert to be provisioned. The state should say "pending" very soon after applying the DNS changes (< 5 min).

Check the (sub)domain periodically in the browser, to see when it starts working (it took me about 20 minutes to give you some anecdotal metric, and it started working before the "pending" label had been resolved in Firebase). Eventually Firebase will switch the state label to "connected" to complete the configuration.