Google Product Forums
Re: Can't enroll in Google Grants
Google Grants Help Forum
Google Grants Eligibility & Program Details
99.9% of the time when this happens it is because you are logged into a different Google account than the one used for the G4NP sign up. This is easy to do and VERY common occurance.
I recommend signing out of Google, then signing in again under the approved G4NP account.
All the best,