iPad Air (2019)
It's not possible to send and receive iMessages
Solution 4 of 5: Your tablet hasn't been correctly set up for iMessaging
You can send iMessages to phone numbers or email addresses if the recipient has a device which supports iMessage. To set up your tablet for iMessaging, you need to activate your Apple ID.
Press Settings.
Press Messages.
Press the indicator next to "iMessage" to turn on the function.
Press the Home key to return to the home screen.