Issue with Automated File Sharing via Graph API – Invitation Emails No Longer Sent

Hello everyone,

I’m using the following C# code to automate file sharing via the Microsoft Graph API:

var requestBody = new InvitePostRequestBody  
{  
    Recipients = driveRecipients,  
    Message = message,  
    RequireSignIn = true,  
    SendInvitation = true,  
    Roles = ["write"],  
    ExpirationDateTime = DateTime.Now.AddDays(7).ToString("o"),  
};  

await GraphClient.Drives[driveID].Items[driveItemID].Invite.PostAsInvitePostResponseAsync(requestBody);  

This approach worked flawlessly until November 14, 2024. Starting from that date, no invitation emails are sent to the recipients anymore. The file sharing itself still works as expected – I can verify in OneDrive that the recipients are listed under the "Sharing" section. However, the notification emails to the recipients are missing.

Also, if I share a file manually, the invitation Mails gets send still.

Has anyone encountered a similar issue or has an idea what might be causing this? Could this be related to a change in the API or some configuration I might have overlooked?

Thank you in advance for your support!