I've refactored the original code and produced a new version. This version uses AJAX with multiple buttons to go through each step.
I'm not very good with github and I don't think I have done the branch correctly!
I've tested it with my v1.4 on PHP 8.0 as well as upgraded my v1.4 to v2.0.4 and used PHP7.4. My site has users and permissions and things worked to bring the manager back up on v3.