You will need to add the Altitude MDM Server to Apple Business Manager by following these steps.
Open the "Devices" menu
Then select "All Devices"
Then click "Edit"
Select "Assign to the following MDM" and in the drop-down select Altitude MDM you created earlier
Confirm the following prompt
The devices are now connected to Altitude MDM for boot up Configuration.
You will now need to configure the device to the Automatic Configuration Profile in Altitude MDM.