NMS app stuck in google pay services

i have a new HTC android 4.0.3 phone. i downloaded and installed the free version of NMS from google.

But then when i tried to upgrade to the paid version, a popup  said something about payment method.

I guess I don't have a payment method at google.

Then the NMS app shows "purchasing from google" and it is stuck.

I tried to stop the google payment service from the settings menu, but it will not stop.

What do i do now?