Can't buy GarrysMod as a gift for a friend?

When I try to buy Garrys mod as a gift while its on sale 75% off, it says an error:

“Your purchase has not been completed.
The payment processor has reported an authorization failure. Please select a different payment method.”

I’ve tried both my Steam Wallet and Paypal - Same error?

Anyone know how to fix this? I wan’t to get it before the sale ends.

idk D: does he have any source games? be3cause garrysmod needs source games to run

Maybe Steam servers are clogged with people buying and downloading due to the sale?
Although I’m not sure that would matter…