Its my first time to purchase something thru credit card in GOG galaxy, its saying that its not yet enabled when itry to check out, so how do I enable credit card payment? help pls. thanks

Try buying directly through the site. Galaxy is in beta and not all the features are enabled.

I tried on the site but it just shows this: :( what can i do?

Try buying without the dlc's.
Did you made another purchase in the past and did it work?

The problem is not buying with credit card, the problem is that you try to buy it as a gift.

There was a lot of credit card fraud (people buying gifts with stolen cards and selling the codes to shady reseller sites) and because of that you'll have to wait three months before you can buy a gift via credit card.

but is it possible he can link his card to paypal and then buy a gift. Can't he?

Oh, Damn. Okay, i feel a bit foolish now, Thanks for the help guys, seem to have found my way now :)

I guess so (but don't know for sure).