To be able to send private transactions/collect fees you will need to set up your router opening port tcp 32348 and be sure you firewall allows xc app trough port 32348. If one of those is set up wrongly your private transactions/mixer fee will not work there is a readme file as well where it explains it in ver 2.49.02
According to portcheckers.com, port 32348 is open and my Windows Firewall allows the XC app. Not sure if there is anything else I should be checking....

For me was the same and could not made them.. I think if you turn off and then back on again your pc the Exception rule of the firewall will need to be done again. If you do not have a rule made in the firewall for the xc app with forwarding port 32348 I would make it If you already have I would disable it and enable it again..
After doing so I can now make 1 to 2 xcs private transactions..I cannot hoever made larger numbers of xc transaction so there might be bugs still or there might be some settings I'm not aware of that you and I made wrong...
Im waiting for an official guide on how to set up a mixer too