I used "JustFly" in late August 2018 to fly to Cambodia, in addition, I had a ticket for a travel companion to join me one week later... both using JustFly.
After booking, but prior to departure, the departure time from my hometown was changed by only a few minutes and I received updated information.
I attempted to check-in with my home departure airline, 24 hours in advance, Alaska Air and was told I had two different confirmation numbers ( I think that is the correct term) and I would not be allowed to fly. I spent literally 6 hours on the phone, making multiple calls to JustFly and I recorded each conversation. The JustFly representatives appeared to be Totally Clueless as to my problem and told me I would have to call the airline in China.
After 6 hours and multiple calls to multiple people, A call to the Chinese airline I was traveling on told me the ticket needed to be reissued, that it should have been reissued when there was a change, but it was not. Eventually, with that information, I again called JustFly and I guess they reissued the ticket, because I did fly.
My companion who was to join me a week later, was denied boarding the Alaska Air because of the same reason. A wonderful Alaska Air agent spent 6 hours attempting to correct the issue, and finally got her on a different flight and arrived one day late.
JustFly is clueless and were horrible!