Admins will then enter the API user credentials into either the Online Intake Clinic Event Appointment block (for displaying available clinic appointments) and/or the Online Intake Appointment block for Office/Staff appointments.
You can of course step through an online intake to reach the point where available appointments are displayed. An alternative is to create an auxiliary process and form, put the process in the Actions menu, and use that on an existing matter on the OI site. The form needs to contain the Online Intake Appointment block, configured with the API credentials, just as your "real" intake form is.
If you have appointment slots configured on the destination site, but no available appointments appear on the online intake, grab the credentials from the Online Intake Appointment block and try logging in on the destination site.
The Online Intake Clinic Event Appointment block does not have a configuration option for "Schedule: Max num of days in the future" like the Online Intake Appointment block has (for staff and office slots). Clinic slots will display as far in the future as there are slots marked as Publish Online. (LS-93090).