In Xporter Permission Scheme, when adding specific Issue types to a Permission Scheme, you can see a list of Issue Types showing with the Project Key, and others without it:
If you are trying to add the Issue Type with your Project Key and it is not showing, this might be related to the type of Project you are working.
If you have a Company-Managed Project, the Issue Type to apply, in the example above will be Subtask, while if you have a Team-Managed Project you’ll have the “Subtask – Project Key”.
This is expected, since Company-managed Projects allow a standardized way of working with Issue Types across multiple projects, while in Team-managed Projects, the issue types are created per Project, which means that even with the same name, each Issue Type has its own ID, and this explains why in the Issue Types dropdown, you see equal names but associated with a different project, because theoretically speaking they are “different” issue types.