@Niziol Derek VANM Thanks for posting in our Q&A.
Please check if you use the primary user to sign in the company portal app.
Based on my test, if I use other user account to sign in company portal app, it will ask to enroll the device again. When I tap on postpone it, it will show the message "this device is not managed" in company portal app.
Please click on the Avatar icon > logout > use the primary user to sign in. Then check if this message disappers.
Hope it will help.
If the answer is the right solution, 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.