@Pete Klevin,Thanks for posting in Q&A.
For your issue, please check the following.
1.Please check if you have blocked Android Enterprise under the device enrollment restrictions in Intune portal.
2.For Android device administrator, Android v10 and later do not support identify corporate-owned devices with IMEI or serial number. For Android Enterprise personally owned work profile, Android 12 and later do not support either.
This error happens if your phone is not detected by Intune as a corporate phone. Make sure you have configured the corporate identifier properly in Endpoint manager by adding the serial or imie number.
Please check your Android version to see if it meets this scenario. If yes, we suggest trying other enrollment method like corporate-owned with work profile to do the enrollment for these devices.
Please check above information, if there is any update, feel free to let me know.
If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.