Webthey should be able to pay the bill thru mpos by typing airtime in the search bar for the sku.
It will provide the amount due but no personal information on the receipt.
Webthe website also gives the option to pay bill as a guest but still requires a tmobile phone number or account number to pay a bill as a guest.
Webnow when i try the guest pay option using my account number, i get “we are unable to accept guest payments from this phone number provided at this time.