The form will not be copied because it resides in another site

Symptoms

When migrating a content type, Sharegate displays the following warning: 

The form located at 'http://myServer/sites/otherSite/newItem.aspx' will not be copied because it resides in another site. In order for the content type to work properly, the site containing the form will need to be migrated.

Error code

Details

When copying a content type, Sharegate verifies if the content type has custom New, Edit or Display forms. If it does, the forms will be automatically copied by Sharegate and the content type will be linked to them at the destination. However, if the forms are in a site different than the content type's site, Sharegate will not copy them automatically. It will instead assume that the form can be found at the equivalent location on the new server and it will set the content type to refer to this location.

Solution

There are 2 possible solutions for this warning:

1. Copy the site containing the form with Sharegate. This way, the form will be found at the location where Sharegate expects to find it and the content type will function properly. The site containing the form can be copied either before or after the site containing the content type. 
2. Edit the destination content type and change the New, Edit or Display form to refer to another location, or create a new form.