Problems setting up Obsidian Sync: "Your subscription to Obsidian Sync has expired"

First, search the help docs and this forum. Maybe your question has been answered! The debugging steps can help, too. Still stuck? Delete this line and proceed.

What I’m trying to do

I am trying to set up Obsidian Sync. I bought the $4/mo version (I have the receipt) but when I try to set up a remote vault, on hitting the “Create” command, I see a message: “Your subscription to Obsidian Sync has expired.” This happens whether or not I supply an encryption password.

Things I have tried

I tried turning off the encryption password.

I tried waiting till the next day.