Can't make any payments on T-Mobile website

I have been unable to submit payment to my T-Mobile account since 23 Oct.  This error I am have is repeatable.  It occurred multiple times (around 7x or 8x) on 23 Oct.  I tried twice again today (30 Oct) and same error keeps happening.  I tried again on 11/13/2021… same problem.  And again today, 11/23/2021… same problem.

Here are the steps I'm doing:

1. Ingresa a https://account.t-mobile.com
    
2. On the /account-landing page, click "Add to balance"
    
3. Select "Make a one-time payment" (I’m using the amount due.)
    
4. Select the "Amount due" radio button
    
5. Select my existing payment method (I’ve deleted and re-added my CC info multiple times to make sure I didn’t enter the wrong info.)
    
6. Scroll through notice and select "Accept and Submit"
    
7. A dialog then pops up.  The dialog says "Processing Order", and then a second or two later, the text "Sending Transaction Details" is added to the dialog.  I'm not sure of the exact wording though, because a second or two later, all the text disappears, so I don't have time to write it all down.
    
8. Finally, I'm left with a completely empty modal dialog box.  The box has a single, pink button, which also has no text.  See the screenshot at the end of this post to see what I see.
    
9. Because this is a modal dialog, there is no action available except to click the mysterious, pink button.  When I do, I am brought back to the /home page.  When I go back /refill-account page, I can see that the payment failed, because I still have an outstanding balance.
    
10. Each and every time I do this, T-Mobile IS MAKING a charge to my credit card.  (Therefore, I know I DID enter the correct credit card info.)  Then, a second or two later, T-Mobile refunds the money back to my credit card.  I have called my credit card company, and they have verified this.  My credit card company is not denying any of the charges or refunds.  The issue is completely on the T-Mobile side.  (I can also see the debits/refunds on my credit card when I login to my CC's website.)
    
    To repeat: when T-Mobile charges my card, the charge is allowed by my credit card company.  Then, immediately afterwards, T-Mobile refunds the money back.  The refund is also allowed by my credit card company.  All these T-Mobile transactions are being allowed.  There is no issue with this credit card, which I use successfully for a many other things.  I use this card everywhere without issues, and I've even used the same card before on the T-Mobile website.  But for some reason, nothing works anymore.  I've tried this in two different browsers (Chrome and Edge) on two different computers, and the error always happens.