This is a config issue, appointment types for waiting lists is controlled by Clinic Team and HCP.
If the waiting list team is not part of a clinic, it will get all the appointment types associated to the HCPs that are part of the team.
If the waiting list team is part of a clinic, it will get all the appointment types associated to that clinic.
You can use the below steps to determine if the waiting list team is associated with a clinic and add relevant appointment types to the clinic first and then they will be available to select on waiting list configuration screen.
Click Menu, then Waiting List Configuration.
Search for affected waiting list.
Click on Green Arrow to Edit the waiting list.
Check the Team and HCP details for the waiting list entry.
If there is a Team for the waiting list, go to Clinic Template/Maintenance for the Team linked to the Clinic.
Add relevant Appointment Types on here and click on Save.
Now go back to the Waiting List Configuration for the waiting list in question and now the added appointment types will be visible.