Good afternoon.

I will describe the problem step by step. There is a mail server. It has a web version of mail (SOGo). Created an account for the meeting room. Created a shared calendar and signed mail users with rights to create entries in this calendar. In mail clients connected calendars over the network with user credentials. When creating an event in the calendar, added participants. Participants receive an email with an invitation. Immediately, when the email arrives to the participant, there are buttons to accept, but as soon as the event is synchronised and added to the calendar, the buttons disappear. Why? An error occurs when clicking on the refresh button. Why? How to set up a shared calendar correctly? Is there any instruction?