I can not make purchases.

Xten808

I have been playing for over a year now. When items are being sold at regular prices I can make purchases. But when the prices become reduced, if I try to make any purchase it would say transaction not complete because I need to sign into a Google account on my device. I have done that and I still can't buy anything.
What do I do? I need help urgently as some items I want to buy are almost expired.
Thanks.