GitHub has paused newCopilot Pro subscriptions
What I missed when I wrote about GitHub Copilot changing to usage based billing is that a few days earlier they paused new sign-ups for Copilot Pro and Copilot Pro+
This also includes existing customers that cancel their subscription as re-subscribing appears to be considered a new subscription.
Since GitHub is rolling out the updated usage based billing starting June 1st I'm guess that this pause will be in affect at least until then.
Update
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This also applies to new self-serve signups for GitHub Copilot Business