Mod/gm-What is this

Whats your Operating System? Did you try to restart your Game after that Error meanwhile? Did you retry to buy them again, when the buying process was interupted with these Error? Were the ZP taken out of your Account or were they still on your account? This might be a Server Sided Error, due some unkown Error. Therefor i think the best Solution is to just try and buy them again. If that doesnt work, you should open a Support ticket, they can resolve maybe that problem and refund your ZP back into your Account, if the ZP was taken out of your Account.
You can contact the Support here:
http://support.z8games.com/webform.aspx