The messages below mean DivePilot refused a change on purpose, because it breaks a rule. Each row links to the article that explains the rule.

Bookings and customers

Message What it means
"The booking is for a different departure than the trip" or "The booking is for a different date than the trip" The booking and the trip no longer share a date or departure. When you seat a booking, one of them was changed after the trip page loaded, so reload the page. When you move a guest who is already seated to another group, their booking or the trip was changed after they were seated, and reloading does not help: change the booking to the trip's date and departure, or take the guest off the trip. See Change a booking's date, departure or type.
"Only reserved or confirmed bookings can be assigned to a dive group" The booking is completed, marked as a no-show, or was cancelled in the meantime. See Booking statuses explained.
"That seat is already taken" Someone seated another diver there after your seat map loaded. Reload and pick a free seat. See Seat divers on the boat.
"Only reserved bookings can be confirmed", "Only confirmed or completed bookings can be marked as no-show" or "Only cancelled bookings can be restored" The status changed after you opened the booking, for example a colleague confirmed, seated, cancelled or restored it. Reload the page. See Booking statuses explained.
"This customer already has bookings or enrolments and cannot be declined" Decline and delete as spam only works for a registration without bookings or course enrolments. Guests who book online land in the same queue, so use Mark as handled for them. See Handle new registrations.

Note: The date, seat and status messages usually mean a colleague changed the same record while your page was open. Open pages do not refresh by themselves, so reload before you try again.

Staff schedule and pay

Message What it means
"This staff member is already scheduled at that time" The person already has a boat trip, a course session, an office or reserve duty, or time off that overlaps. Time off, and a duty without times, count as the whole day. See The staff schedule.
"This staff member is missing the required role" Teaching a course or a session needs the Instructor role, and reserve needs Instructor or Divemaster. Someone with no roles at all is not restricted. See Manage your team's accounts.
"This staff member already has time off in that period" Two time-off entries of one person cannot overlap. Edit the existing entry instead. See Duties, reserve and time off.
"The pay period covering … is closed - reopen it before changing earnings" You added or deleted an adjustment on a day inside a closed pay period. Reopen the period first. See Pay, earnings and pay periods.

Courses, pools and your profile

Message What it means
"The course has reached its maximum number of students" The enrolled students, not counting withdrawn ones, already fill Max students. Raise the limit or withdraw someone. See Enrol students.
"The pool is already booked for this time by “…”" Another block or course session on the same pool overlaps that time, and the message names it. Back-to-back bookings are fine. See Pools and pool bookings.
"This pool still has upcoming bookings" A pool with bookings today or later cannot be deleted. Move those bookings first. See Pools and pool bookings.
"Your current password is incorrect" Under Edit profile, the Current password does not match. If you forgot it, sign out and use Forgot password?. See Your profile, language and password.

A message not listed here

General messages such as "Something went wrong" or "ThrottlerException: Too Many Requests" are explained in Error messages and pages that do not load. If a message keeps blocking you and no rule explains it, see Contact support and check the system status.

Did this not answer your question? Contact support