After installing the mobile ClassLink app, you must set the current district in order for login to function correctly.
1. Start the ClassLink app then click the arrow in the top left corner.
2. On this screen click in the search field at the top of the window and type in "Grapevine". This should limit the list down. Select "Grapevine-Colleyville ISD" from the results.
3. You should be taken back to the GCISD login page where you can try logging in again.
If you are still having issues logging in please submit a support ticket. Include as much information as possible, especial the name of the user trying to log in.