CiviCRM/Joomla troubleshooting

I have an immediate need for someone with strong experience with CiviCRM 5.50.3 and CiviEvents, running on Joomla 3.10. The workflow for online event registration is screwy and users get a permission error when submitting reservation or when returning to merchant from Paypal.
Also, need to have site patched with relevant Civicrm security updates.