Microsoft Graph Calendar API 403 Forbidden Error Occurring for Some Users Since October 11, 2024

Question

We have integrated Microsoft services into our developed application, allowing users to make calendar reservations. After a reservation is made, we use the Microsoft Graph Calendar API to write events to the user's calendar. Since around October 11, 2024, we have encountered a recurring issue where some users experience errors when writing to the calendar. The API returns a 403 Forbidden error, although the majority of users are unaffected and the integration works as expected for them.

We would appreciate any insights or guidance on potential causes for this issue.

Answer 1

Hi ps test,

Thank you for contacting Microsoft!

The 403 Forbidden error with the Microsoft Graph Calendar API can occur due to several reasons:

1. Permissions Issue: Ensure that the affected users have the necessary permissions to write events to their calendars. The required permissions include Calendars.ReadWrite for both delegated and application permissions
2. Tenant-Specific Issues: There might be tenant-specific issues affecting the permissions or configurations. Verify that the affected users are correctly configured within the tenant and have the appropriate licenses

Since the issue is restricted to specific users, I recommend raising a support case with Microsoft Graph. A Support Engineer will be able to assist you better.

You can raise support ticket from New support request - Microsoft Entra admin center or https://admin.microsoft.com/#/support/requests

Hope this helps.

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