A Customized Help Link is a new Office 365 feature. Microsoft will begin rolling this feature out soon.
This message is associated with Microsoft 365 Roadmap ID: 49288.
How does this affect me?
When a user is blocked from sharing externally by policy, you can now provide a “learn more” link that will be surfaced in the error message. This link can be used to explain company policies on external sharing or it can direct users to internal portals to request policy changes.
This feature can be configured using SharePoint Online Management Shell. Once you are connected to the SharePoint Online service, you can run Set-SPOTenant –CustomizedExternalSharingServiceUrl (Insert URL here)
Microsoft will be gradually rolling this out over the course of the next week, and the roll out will be completed for worldwide production environments by the end of March 2019. This feature is not currently available for GCC organizations.
What do I need to do to prepare for this change?
There is nothing you need to do to prepare for this change. Please click Additional Information to learn more.Additional information