PayPal email address

Hi, I’ve created a couple of buttons with your plugin and inputted my client’s email address as the receiver of the donations. It worked fine on the staging site, but it’s not working on the live site. When I use my email address, it works. When I use theirs, it says they don’t have a valid account (they do). I’ve checked their email address and PayPal account and everything is fine on that end.