I’d like to ask anyone having this issue, is the workout you’re trying to sync to Zwift a structured workout from Training Peaks that you purchased? If so, I need to let you know that these workouts don’t work with Zwift. I helped someone with this issue a while back, and he shared it in our Community Forums. Here’s what he had to say:
"So it seems some of the “workouts” you might get in a purchased training plan on Training Peaks aren’t actually workouts but performance “tests”. These tests, by their nature, can’t have the targets filled in ahead of time and thus Zwift can’t use them as a “structured workout”. "