This article contains information that applies when you use the OneDrive for Business sync client (groove.exe).
NOTE: To determine which OneDrive sync client you're using, see the article, Which OneDrive sync client am I using?
When an external user tries to sync a document library by using the OneDrive for Business sync app for a SharePoint Online site collection or sub-site, the user is repeatedly prompted for credentials and receives the following message:
Call us Overprotective.
To work around this issue, enable sharing for the root site collection. To do this, follow these steps:
Browse to the SharePoint admin center.
On the site collections page, select the check box next to the root site collection. For example, select the check box next to https://contoso.sharepoint.com.
On the ribbon, click Sharing.
Select Allow external users who accept sharing invitations and sign in as authenticated users, and then click Save.
Be aware that by enabling sharing at the root site collection, users can share resources on the site with external users. For more information about external sharing, go to Manage external sharing for your SharePoint Online environment.
Replace the contoso placeholder with the domain that you use for your organization.
This issue occurs because the OneDrive for Business sync app checks sharing properties at the root site collection (https://contoso.sharepoint.com). Although the site collection where the external user is trying to sync has sharing enabled, the OneDrive for Business sync app validates that sharing is enabled for the root site collection.
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