E0003

Verifying was refused because no GitHub account is connected to the person's account.

Erroneous example:

$ crab billing verify
Error: 403 [E0003]: verifying takes a GitHub account connected to yours

Verifying reads the GitHub account the person signs in with. An account made by signing in with Google has none until GitHub is connected to it, as a second way to sign in.

crab billing verify prints a link when it cannot verify; the page it opens connects GitHub and verifies in one go. Signed in on the web, the account's Usage page has Connect GitHub too.