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If instead the OC must be published to an app catalog with an on-premises SharePoint Server, the following installation steps must be followed: https://docs.microsoft.com/en-us/office/dev/add-ins/publish/publish-task-pane-and-content-add-ins-to-an-add-in-catalog. This documentation also includes how to access the OC from the client side, and thus, you can skip to the last picture in on this page. Please be aware of the limitations of following this approach: Digizuite™ Office Connector 2.0 - 0. Requirements.
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