I recently flew out of CUN on UA, my airline. I couldn't check in at the kiosk or online, an agent assisting me stated that the tax had not been paid. I had selected payroll deduct when making my listing, so I canceled that and rebooked, paying the departure tax upfront with my credit card. Even that did not help. Finally, after waiting in line, I was able to speak to an agent at the counter and was told I had to pay an additional $21 on top of the departure taxes already collected via EmployeeRes (equivalent of Travelnet). The last time I experienced something like this was upon leaving Tegucigalpa when flying DL in 2013. I spoke to some of my co-workers once back in the office and they stated that unfortunately, paying that additional $20 or so is required, upfront & on top of the already assumed departure taxes at that.