Everything. Initially, my flights had changed and I e-mailed Travel Up to ask rather than the other way round. When organising a new ticket I dealt with Sofia Smith who I found unresponsive and unclear in her written communication (see e-mails). Three weeks had passed in between the changes and me being issued a new ticket, and that's because I had to chase her up. I found this highly inconvenient since I do not live in the UK and am a very busy person. Also calling and finding a time to do it is not ideal given the time differences. In addition, the flight changes I was offered in the end were worse than what I originally booked and paid for. I will not be using Travel Up again.