If you see this message that asks for Activation Information please click the "Self-Service" button under "Sign In."
If you see this message that asks for and email or password, please quit the Mosyle Manager app (type command Q on your keyboard) and then reopen the Mosyle Manager app. You should see the "self-service" button from there.
If you get the message that the iPad is too full for the download check your iPad storage: Settings > General > iPad Storage.
Save any old images or work to your Google Photos/Google Drive and delete them off your iPad. Then try again.