Processes in Microsoft 365 for setting up Office apps, redeeming product keys, and activating licenses.
Hi Peter,
When registering the product key, did you turn on the auto renewal by any chance? If so, then its normal since if you turn on auto renewal, you will be given additional 3 months, thus, a payment method is required that will be used later on for the auto renewal.
Otherwise, please provide a screenshot of the prompt for asking payment method for my reference.