To verify Push Notification works with your forum. Visit {Your forum root url path}/mobiquo/push.php using a Web Browser. You should receive a message 'Tapatalk push notification test: Success'. If you do not receive this message, Tapatalk can still work but without push notification feature.
Get help here.
If you were using a version of the vBulletin 5 Tapatalk Plugin that came before Version 1.0.0, you should uninstall the Tapatalk Product from the vBulletin 5 AdminCP and also delete the 'mobiquo' folder. You may then continue with the steps listed above.