I am developing an app to read the calendar and render it with fullcalendar, the error comes when logging in and the redirect uri gives an error

I’m having trouble with recurring events in my calendar app. Events that repeat several days within a week and extend over several weeks appear sporadically. Could someone help me understand why events are sometimes missing during certain weeks?

Through API I read my outlook calendar and show it in a calendar from the FullCalendar library.