I am receiving the same message as you "this item can only be saved by one person". I only have one email account. I have only downloaded Google Pay once. Tried downloading from the online link rather than the email link too, but same problem. Hopefully HWT will have a solution!
Mrs T says try a different browser, and check that you didn't do what I did (which was create a google pay account when google pay started out then forgot I'd done it). And make sure your google pay account is connected to the right email address (that was actually how we realised what had happened; I have two active email addresses and, well you can guess the rest).