I have also tried 'Transfer Out' from the Vercel account where I purchased the domain and 'Transfer In' to my other Vercel account, which produces the following error:

The entered domain is not transferable (reason: "Domain already exists in Vercel Inc's account").

I'll pass this along to the Domains team, thanks for reporting

Looks like this fix is in active development, but might be a day or two before it's shipped

Thanks for the update, Jacob. Please let me know when I should give the domain transfer another try.

Same problem. Waiting for a fix

It's been three days. Any updates?

Is that problem fixed? I still have the problem

Hi there, we're sorry that you faced this issue. Our team is still looking into it and we'll update you as soon as we resolve the issue.

This should be fixed now, can you try again?

Hi, Jacob. I'm afraid not. When I enter the team name to which I want to transfer my domain on this screen, I only ever receive the error "Moving to account domain [team name] is disallowed". So, it's now failing even before I receive a notification of the transfer in my other team account.

It has now been 11 days since my original post. At this rate, I fear I'm going to have to transfer the domain out to another registrar and then back to my other Vercel team account (both of which cost money). Is this the only solution for now, or is there a fix in the works?

Can you try again making sure you're using the team slug?

You can find it in the URL bar or in your team settings, in this case my team slug is rhyssullivans-projects

That error only occurs if you're putting in a user slug, I've double checked our logic to ensure that it's right

Cheers, Rhyssullivan. The long-broken 'You may approve the request by clicking the following URL' link finally worked.