Sync issues on shared sharepoint folders with subcontractors

I have subsequently been on a call and think it is a problem at his end. He appears to have multiple licences on his computer and also one of these may only be partially set up correctly, so I am going to leave him with web access as it will be down to him to sort his own computer out. Thanks though.

Hello @Kaye Davis, 

Good day! I hope you are doing well. 

Based on your description, I understand that your subcontractors can access the shared SharePoint folders on the web and see the Sync button, but when they attempt to sync the folder to their OneDrive/File Explorer, they receive an error stating that OneDrive is unable to complete the action. 

Please let me know if I misunderstood any part of your issue or if there are additional details you’d like to share. 

To help us provide the most accurate and effective solution, could you share a bit more detail about your setup: 

• What type of email accounts are your subcontractors using (Microsoft 365 work/school, or personal accounts like gmail, hotmail, yahoo,…)? 
• Have the subcontractors been successfully added as guest users in your Microsoft Entra ID (Azure AD) directory?  
• Or are they using internal accounts that your organization provided? 
• Are you sharing the folder using a link that requires sign‑in, such as “Specific people”? 
• Has external sharing been enabled both at the organization level and on the specific SharePoint site? You can check this setting by following this instruction Change the sharing settings for a site - SharePoint in Microsoft 365 | Microsoft Learn 
• Do you happen to know that your tenant have any Conditional Access policies in place that might restrict access for external users (e.g., location/IP restrictions, MFA requirements)? You can ask your IT admin for confirmation. 

This additional context will help us understand your environment and the steps already taken so we can tailor the guidance to resolve the issue effectively. 

I apologize if I could not jump straight to a solution. I want to avoid suggesting anything that might be inaccurate or unhelpful. Once we have the details above, we’ll be able to assist you more effectively and guide you toward the right resolution. 

Looking forward to your response so we can get this sorted out for you together. 

If you have extra questions about this answer, please click "Comment". 

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For subcontractors to sync shared SharePoint folders to File Explorer with OneDrive, the following conditions must be met and checked from the site side and the user side.

1. Confirm the site is enabled for syncing
   • Have the subcontractor browse to the exact SharePoint document library/folder.
   • They must see a Sync button in the library toolbar.
   • If they see a page saying "Which library do you want to sync?", the site is not configured for the current OneDrive sync app. In that case, the site owner/admin must configure it to use the new sync client as described in Let users sync SharePoint files with the new OneDrive sync app (linked from the documentation).
   • If the Sync option is missing entirely, the site owner needs to enable offline availability in library settings (via Library settings > More library settings > Advanced settings > Offline Client Availability) as indicated in the SharePoint sync troubleshooting article.
2. Verify they can access the library in SharePoint Online
   • Ask subcontractors to:
     1. Sign in to Microsoft 365 with the account that has been shared to.
     2. Browse to the SharePoint site and open the document library/folder that was shared.
   • If they cannot open the library or documents in the browser, permissions are insufficient and must be adjusted on your side.
3. Ensure they are using the current OneDrive sync client
   • When they click Sync, the browser will request permission to open Microsoft OneDrive. They must allow this.
   • The files then sync to a folder on their PC named after the organization (for example, %userprofile%\Contoso), and this is automatically added to File Explorer. They cannot choose a different local path.
   • If they see the old Groove client icon or an error about libraries not being supported, they need to upgrade to the new OneDrive sync app as per the guidance linked from the sync articles.
4. Check for library or file conditions that block sync
   • If they see a lock icon on synced files, the library may be read-only for them (required checkout, required columns/metadata, or no edit permissions). In that case, changes from their computer will not sync; permissions or library settings must be adjusted by the site owner.
   • If the site name or library path includes unsupported characters for Windows folder names (for example, :), the library cannot be synced. Renaming the site/library to remove unsupported characters is required.
5. Confirm OneDrive is running and configured on their device
   • On Windows, they should see the blue OneDrive cloud icon in the notification area. If it is not visible, they should start OneDrive from Start > search for OneDrive.
   • If OneDrive is running, clicking Sync from the SharePoint library should attach that library under the organization folder in File Explorer.
6. If sync still fails
   • Have them verify they can open and edit files in the browser; if not, fix permissions.
   • If they can work in the browser but sync still fails, they should follow the SharePoint Online sync troubleshooting steps, starting with confirming access to the site and library and checking for the Sync button and any special messages.

From your end as the owner:

• Ensure the subcontractor has at least read access to the library and that Offline Client Availability is enabled in the library’s advanced settings.
• Ensure the site is configured to use the new OneDrive sync client (if users see the "Which library do you want to sync?" screen, follow the admin guidance in the linked article to enable the new client).

References:

• Sync SharePoint and Teams files with your computer
• Sync SharePoint files and folders
• Fix SharePoint Online sync problems