B2B Invitations Blocked Due to Suspicious Activity – Unable to Send Guest Invites via Microsoft Graph API

We are currently facing an issue with B2B guest invitations in Microsoft Entra ID.

We are using the Microsoft Graph Invitations API:

POST https://graph.microsoft.com/v1.0/invitations

Initially, invitations were working correctly, but after sending around 100 invitations in a short duration, all subsequent requests started failing with the following error:

{   "error": {     "code": "Forbidden",     "message": "Invitations are blocked for this directory due to suspicious activity. Please contact Microsoft support for help.",     "innerError": {       "request-id": PII",       "date": "2026-05-20T07:40:54",       "client-request-id": "PII"     }   } }

We have already verified the following:

• External Collaboration Settings allow guest invitations
• Cross-tenant B2B collaboration settings are set to “All allowed”
• The issue occurs for both API-based and manual invitations
• Invitations were legitimate business invitations
• We have stopped sending additional bulk invitations

If any Microsoft moderator or community member can help review or remove this restriction from the tenant, it would be greatly appreciated.

We would also appreciate guidance on:

• Whether this restriction is temporary
• Typical recovery timelines
• Recommended steps to get the tenant unblocked
• Best practices to avoid triggering this restriction in the future

Any help or suggestions would be greatly appreciated.