In the JIRA documentation ...
Sample 2 : Importing links to existing issues
The previous way does not work for this situation, it should to be imported from System> External System Import.
I have not found these menu(s) options presented to a Project Administrator (Jira v8.5.6)!
Q1. Are additional user permissions required to access this capability?
Q2. If so are these system wide and unlikely to be granted in a large enterprise setting?