Invitations are blocked for this directory due to suspicious activity. Please contact Microsoft support for help.

The error indicates that invitations are being blocked at the directory level due to suspicious or policy-restricted activity. In this situation, self-service changes in Microsoft Entra settings (such as external collaboration, cross-tenant access, or allow/block lists) are not sufficient; the block must be removed by Microsoft support.

To proceed:

1. Open a support request from the Microsoft 365 or Azure portal as a tenant administrator.
2. Clearly state that invitations are blocked tenant-wide due to suspicious activity and that bulk B2B invitations are being prevented.
3. Work with the support engineer and Data Protection/Compliance teams as directed to verify tenant ownership and remediate any policy or acceptable use concerns.
4. After Microsoft removes the block, validate that external/B2B collaboration settings (External collaboration settings, Cross-tenant access settings, and any allow/block lists) align with the organization’s requirements so that invitations can succeed.

If external invitations subsequently fail with messages such as “This invitation is blocked by cross-tenant access settings” or “Guest invitations not allowed for your company,” review and adjust:

• External collaboration settings and collaboration restrictions (for example, allow or deny specific domains).
• Cross-tenant access settings for B2B collaboration.
• Microsoft cloud settings if collaborating across different Microsoft clouds.

References:

• Error: ResponseStatusNotOK when sharing a SharePoint or OneDrive site
• Allow or block B2B collaboration with organizations
• Design Tenant Configuration
• Troubleshoot common issues with Microsoft Entra B2B collaboration
• Error "This page has been blocked as it violates the Acceptable Use Policy"