A service or service task can belong to only one appointment.
For example:
- Service 1 has service tasks ST1, ST2, ST3
- Service 2 has service tasks ST1, ST2, ST3
You can split these into different appointments (e.g., Service 1 → Appointment A, Service 2 → Appointment B, or mix service tasks across appointments), but a single service/service task cannot be added to more than one appointment.