Selected user account does not exist in tenant 'Microsoft

The error indicates that the account is no longer recognized as a valid user in the tenant that hosts the SharePoint resource, so SharePoint/Entra ID cannot sign it in.

In Microsoft 365 this typically happens when:

• The account was never (or is no longer) provisioned in Microsoft Entra ID for that tenant, and
• The tenant uses Conditional Access or other policies that require the user to exist as a guest or member before access is granted.

To resolve it, the tenant admin must do one of the following:

1. Ensure SharePoint is integrated with Microsoft Entra B2B
   • The organization that owns the SharePoint site should enable SharePoint integration with Microsoft Entra B2B so that sharing invitations correctly create guest users in Entra ID.
   • This ensures that when a site, list, or library is shared, the guest account is provisioned and can satisfy Conditional Access policies.
2. Have the admin explicitly add the account as a guest user
   • Ask the SharePoint/tenant administrator of the organization that owns the site to add the email address as a guest user in their directory (Microsoft Entra ID).
   • After the guest is added, an invitation email is sent. Accept the invitation, then try accessing SharePoint again using the same account that was invited.

If the admin confirms that the account is already a guest, they should:

• Remove the existing guest entry (if it is in a bad state) and re-invite the user, then have the user accept the new invitation.

This issue is caused by changes in the SharePoint sharing back-end where sharing via the Permissions page may not automatically provision the guest in Entra ID, so only an admin-side fix (B2B integration or manual guest creation) resolves it.

References:

• Error "Selected user account does not exist" when new guests access a SharePoint resource