We apologize if you are having issues with gTunes. Please read the common issues below, and if you still have an issue, contact support! Thanks for trying gTunes!
Unfortunately Apple doesn't allow apps in their Mac app store that prevent iTunes from detecting when the Play/Pause key is pressed.
There is a way to disable this iTunes functionality, which you can read more about here:
You must be in the United States to activate Google Music on your Google Account. Once this has been done initially, it should continue to work from other countries.
You can reach support by logging a ticket at: http://support.altusapps.com