After logging in, I was able to set my credit card. Of course, I was also *not* able to set my credit card, because although I got my Apple *Developer* account successfully moved from USA to Canada this past week, apparently my *Apple TV* account, on the same Apple ID, is still USA. So it would not accept my Canadian credit card because it didn't have a valid USA address. Because my address is not in the USA. It is in Canada.