Entra ID Enterprise app SSO login using guest account fails AADST550105

Hello Steven Gill,

The error AADST550105 occurs when a user is not assigned to the application under the Users and groups section, and the application has the "Assignment required" setting enabled.

When this setting is enabled, users must be explicitly assigned to the application—either directly or through a group—to gain access. If a user isn't assigned, they won't be able to sign in to the application in Microsoft Entra ID.

Resolution: Assign the guest user to the application under the Users and groups blade. For guidance, refer to the Quickstart: Assign users to an app.

To assign a user account to an enterprise application:

1. Sign in to the Microsoft Entra admin center as at least a Cloud Application Administrator.
2. Browse to Entra ID > Enterprise apps > All applications > Select the application
3. In the left pane, select Users and groups, and then select Add user/group.
4. On the Add Assignment pane, select None Selected under Users and groups.
5. Search for and select the user that you want to assign to the application. For example, ******@contoso.com.
6. Select Select.
7. Select None Selected under Select a role and then select the role that you want to assign to the user. For example, Standard User.
8. Select Select.
9. Select Assign at the bottom of the pane to assign the user to the application.