Thanks for sharing the details with us.
As of now, you need to delete previous user device from App42 data base to register a new user on same device. For deleteing the user device Go to AppHQ console -> select push notification -> Users -> Now select the user you want to delete -> click on UnSubscribe Device. Or you can use deleteDeviceToken API for deleting device token .
It looks like you have calling store device token method with wrong device token. Kindly verify that your device token is correct and let me know if you still have this issue.
If possible then share your project file with us at firstname.lastname@example.org. It will help us to provide quick solution.