If the alert message is displayed as shown in the image below in Employee Directory 365, please refer to the steps provided below.
Go to portal.azure.com as an AAD admin.
- Click App Registrations.
- Locate the SharePoint Online Client Extensibility Web Application Principal and open it by clicking on it.
- Look at "Certificates & secrets" in the left-hand nav, and delete the only secret that exists.
- Wait for approximately 1 minute to allow the deletion to propagate.
- Go to SharePoint Tenant Admin > Expand Advanced in the left nav, click API Access.
- Allow the page to load; keeping it open will ensure the creation of your app registration.
- Return to Certificates & Secrets in the Azure portal to verify the presence of your newly generated client secret.
- Visit Employee Directory 365 to verify whether the system is successfully pulling users or not.