Can't add device to account

Every time I go online to add my phone, it recognized the serial & phone number, but then says it can't process payment? I wasn't trying to buy anything. I just want to add it to my account
https://www.straighttalkwirelessforum.com/
https://www.straighttalkwirelessforum.com/viewtopic.php?f=6792&t=1275846