The admin credentials set in the Admin Menu have to match the current admin credentials of the printing device. The embedded terminal uses these credentials to access the printing device's settings and to enable unlocking the printing device's panel via the System settings button.
If you have changed the default admin credentials of the printing device, you need to set the new credentials here.
To set the admin credentials:
Tap Username, then type the new admin username, and click OK.
Tap Password, then type the new password, and click OK.