Before you add the Sub Workspaces Webpart to your template navigate to your workspaces list and create a new column.
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Give it a name, set it to be a lookup column, set the source to the Workspaces list.
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Press OK.
Go to your template sitecollection and press "PAGE" on the page you want to add the webpart.
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Now click on the edit page link.
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Select the webpart zone and click add a Web Part
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Select the Sub Workspaces AppPart and press the Add Button.
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The webpart has been added to you site. click on Edit Web Part
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Select the CM365 Category. In the input field add the internal name of the newly created column. Press OK.
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Press Stop Editing.
After you have finished please navigate back in the template list and save the template.