You can delete self-service and re-download,
In my case, it works.
Incase someone comes across this, it's a known issue.
Issue # PI120534
Description
In Self Service, when prompted "Self Service Would Like to Send You Notifications" selecting "Don't Allow" causes Self Service to fail to load content and display an error message.
Easier than removing and reinstalling the Self Service app is to:
For iOS 18
Go to the Settings app > Apps > Self Service > Allow Notifications
For iOS 17
Settings app > Self Service > Allow Notifications
Easier than removing and reinstalling the Self Service app is to:
For iOS 18
Go to the Settings app > Apps > Self Service > Allow Notifications
For iOS 17
Settings app > Self Service > Allow Notifications
Thanks for pointing out the notifications fix @red_beard !
Noticed same issue on some new/recently wiped iPads. An additional step that could remove the potential of this error sneaking up on future devices could be to create a config profile to enable notications for Self Serve and scope it to your iPad fleet

Thanks again @red_beard !