Fatal error messages are pretty normal forcing you to continue to pay for support. I have other addons for Codecanyon and never had as many issues as I've had with this one.
Support team will help if your support is not expired.
I think this addon needs permanent support. Look else where
Author response
We have not received any message from you since 2015 when you started to use our product. We constantly test our code in https://demo.userproplugin.com. All bugs we found or our customers report is fixed with highest priority ASAP. We are always ready to collaborate with our clients and help them to solve every problem and compatibility issues with other WordPress products. Our support desk working every business day 8 a.m. - 5 p.m. (GMT +2). We kindly ask you to leave us a message in a support ticket and share more details.
