MiaB automatically generates an Apple Configuration Profile file with the file name extension “.mobileconfig” that can be downloaded from the “Automatic configuration” section of the “Mail Instructions” page of the MiaB administrative website. The Configuration Profile file generated by MiaB version v0.26c contains an incorrect Principal URL field value in the Calendar record.
The erroneous current field value is: /cloud/remote.php/caldav/calendars/
The field value should be: /cloud/remote.php/caldav/principals/
Until this MiaB problem is fixed, the automatically generated Configuration Profile file can be edited using the free Apple Configurator 2 application that can be installed using the macOS App Store application.