The problem may occur when someone other than the practitioner with whom the appointment was made tries to initiate the video call. Only that specific practitioner can start the video appointment using their own user account.
If a different practitioner wishes to start the consultation, the appointment needs to be transferred to them first.
Furthermore, the video appointment is only available around the time that the appointment was scheduled. If you try to join the video call before or after the appointment start/end time, you may see a message that the call is not available. If you try to join the call on another day, the button to join the call will not be visible at all.