Why does Paypal hate my Mastercard when sending money to other Paypal users?

[Avy9096]

I receive a request for money or want to send money to another user.  

I go to do so.  50% it works and I can click on my Mastercard.

The other times...it just says PLEASE ADD A PAYMENT METHOD.

AAAAAAAAAAAAARGH.

I'm literally dying.  Someone help me.