cant seem to complete orders when using money from my wallet, it says $0.00 left to pay but it the complete purchase button is still greyed out or faded.

Pls help, i wanna buy a game b4 the sale ends.

Check if wallet funds currency are same as store currency.
Put in the cart and remove it from the cart then try again.
Contact support on gog's browser page.

Check if you are trying to buy a DLC for a game that you don't own on Gog. That's one of the cases when the complete purchase button is greyed out.

iits not a dlc, but a stand alone expansion, sales over now, but it was NWN daggerfal remastered, it doesnt say it needs the original, i have the original Diamond version, so it should go thru, but it didnt.

But its ok tho, sales over cant get it no more, spent my money on something else, cause i could complete those purchases with my wallet funds, and not the NVW expansion remake by beamdog.

Um, that's wrong on both accounts.

As can be seen on the game page (www.gog.com/game/neverwinter_nights_darkness_over_daggerford) the expansion isn't standalone but requires the Enhanced Edition of NWN and the discount is still active. According to the sale page the sale is running until midnight so there is still more than 7 hours time to buy this on a discount.