So can I use google play credits in google pay app?
 

Some idiot gave my son $50 gift card for google play. I have only paid once for phone app and have no idea what to do with the rest - $47 . Can this credit be used with google pay?

As far as I know, you can only use it on google play...

You can buy & subscribe to content & services on Google Play.
https://support.google.com/googleplay/answer/113409

Cheers,
z