Shared calendar problem

Hi, I use Mailcow through SOGO. Another user shared a calendar with me, allowing me to add and remove objects. I installed the OneCalendar mobile app and added my Mailcow account via CalDAV. When I check the account details in OneCalendar, the shared calendar is visible. Unfortunately, when I add a meeting in OneCalendar, I can't select this shared calendar. I only see calendars from my Mailcow account in the list. How can I select a shared calendar when adding a meeting in OneCalendar?