Sometimes I need a day off/vacation. Is this possible when working with a trainer?

Option 1.

Applies to Base/Top cooperation with JacaCoadhAPP.

Yes, an athlete training with JacaCoach has the option to report days off.
This should be done well in advance, before the trainer plans the training.
  If necessary, at the last minute, you can use the tool to postpone training (within a week).

Option 2.
“Training for today”
Do not draw a training on a given day, and if you have purchased a larger number of trainings, take a day off. On the next possible day, do the overdue one, moving the rest by one day.