What type of payment method are you trying to add?
What error code or message are you receiving?
please enter a valid credit card number
What region is your account set to?
What region do you physically connect from?
What region is your payment method's billing address in?
I tried setting up xbox live on my console and it said Can't authorize the selected payment option. Please select a different payment option or add a new one, so I tried to do it on the website and it said 'please enter a valid credit card number'