I've had the same issue today and a few months ago. I was able to pay just fine using the mobile app, but as soon as I enter my valid CC number on the online pay portal (windows 10 PC Chrome browser) It's flagged as invalid. I definitely entered it correctly (I tried about a dozen times to make sure). This is a bug on the site. There is a mathematical check that you can do to determine if any CC number is valid. It's called the Luhn Algorithm. It doesn't tell you anything about the account holder or the funds, just that the number itself is a valid card number. Not all 16 digit numbers are. I strongly suspect that this check is failing, and it's likely run on the site itself before sending the number to the server. I'm not sure how to submit a big report to the T-Mobile web portal IT, so this is the best I can do. TMO_Chris, or another T-Mobile representative that sees this, If there is no open issues with online payments, go ahead and open one. If you need more info for debugging the
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