Symptoms
When trying to copy an item, Sharegate displays the following message:
The "Application_Name" Microsoft 365 Application is unavailable at the destination. Please add it through the SharePoint app store.
Error code
AN-035-171
Details
This error occurs when Sharegate tries to copy to an element that requires a specific application to a SharePoint online site. The error means that the application is not licensed for the destination tenant.
Solution
In order to add the application to your SharePoint online site, you will need to get the app from the SharePoint app store:
In your browser, navigate to your destination site, then click on the gear icon at the top-right of the page.
Click on Site contents.
Click on "add an app".
Write the name of the application in the search box and press enter.
A message should appear to tell you that no app was found on your site, but that a result was found in the SharePoint store.