I've set up everything according to the documentation:
For the certificate provisioning process to proceed, all of the following conditions must be met:
- The DNS records for your domain must reference the IP address of your load balancer's target proxy,
- Your target proxy must reference the Google-managed certificate resource.
- Your load balancer configuration must be complete, including the creation of a forwarding rule.
With a correct configuration the total time for provisioning certificates is likely to take from 30 to 60 minutes.
It's been 2 hours.
I managed to get a reply from someone via https://issuetracker.google.com/issues/117900454. I was ignorantly using Cloud DNS' "CNAME" to point to my IP address instead of using an "A" record. Everything is working now.