This article explains how to update your Apple DEP Token which expires each year. You may also need to update your token to resolve an issue where the expiration date shows as "unknown" for one of your tokens shown in the Settings / Apple DEP.
In the Device Console, go to Settings > Apple DEP:
1. Click on the name of the DEP account.
2. Log in to your Apple School Manager (ASM) account and click your name/email address at the bottom of the left menu, and then select Preferences.
3. Select the MDM server associated with the account in Device Console that you selected.
4. Now select Download Token.
5. Click Download Server Token.
6. Back in Device Console > Apple DEP select Choose File and upload the server token from ASM.
7. Once the file is uploaded, click the Update DEP settings button at the bottom of the tab.
Once the operation is complete, you should see new expiration date and a current Last Sync time.