Unable to pay for game pass as gift

Very frustrated. Have been trying to gift game pass to my son for Christmas as well as forza horizon 4 ultimate edition.

I have:

set up outlook acxount

put in payment details.

cannot pay

seached in vain the very unhelpful “microsoft help” pages

gone through his xbox settings to allow him to receive gift card vouchers

read thread about using paypal

made paypal account

re-tried

still no joy with paypal

all i get is cannot process payment....

Please can someone help me

:)