NGCVU

I recently bought a giftcard through the forum section ''Vouchers'' I redeemed this giftcard to be able to buy a script. Whenever I go to my cart to purchase the script it doesn't give me the option to purchase with my balance which is enough when I check my balance. They only allow me to purchase with PayPal which is no option for me but I bought scripts like this in the past with no issues. Why I can't purchase it now?

Could I try out the perfect pest control? Would appreciate it!