Hi @Robin Ganderton ,
Let's work through some steps to address this issue:
1.Verify Organization-Level Sharing Settings:
- Go to the SharePoint Admin Center and sign in with your admin account.
- In the left-hand menu, select Policies > Sharing. Ensure that the sharing settings are set to the desired level
2.Review Site-Level Sharing Settings:
- In the SharePoint Admin Center, click on Sites > Active sites.
- Choose the site in question. Click on the Sharing button in the ribbon. Ensure the sharing setting aligns with your organization's policy.
3.If saving the above two settings does not work, try disabling external sharing in SharePoint Online using powershell:
https://www.sharepointdiary.com/2017/05/how-to-disable-external-sharing-in-sharepoint-online.html
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4.Investigate Potential Policy Conflicts(Conflicting policies can override your sharepoint settings.):
- Check Microsoft Entra (formerly Azure AD) External Collaboration Settings: Review and adjust them as necessary to ensure they don't conflict with your SharePoint settings.
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