We are having hybrid exchange setup. We are trying to read the user calendar using the Microsoft Graph API and when trying to fetch the user calendar of an on-prem exchange, Graph API returning a 401 Unauthorised error. The same works fine with an Exchange Online user calendar. The application has all necessary permissions (Calendars. Read, Calendars.ReadWrite). We are able to fetch on-prem user calendar by login into Microsoft graph explorer (https://developer.microsoft.com/en-us/graph/graph-explorer) ,but the same not working if we are using Graph API.
Please help us with the resolution.