My problem with this solution was that I have signed in to Tailscale via my Google account, and I have to buy Mullvad through Tailscale, linking my Google account to the Mullvad account.

What I wanted to do was have my own Mullvad account and route Tailscale through it, but that wasn’t possible, I had to have Tailscale manage Mullvad, which just didn’t sit right with me.