The Rebbe directs Rabbi Z.S. to a previous letter from the Frierdiker Rebbe, which clearly supports his travel to Ireland, leaving no room for doubt. He blesses him with success and encourages viewing the trip not just as a livelihood opportunity but also as a means to spread Chassidus in Ireland and beyond.
https://www.torahrecordings.com/rebbe/004_igros_kodesh/cheshvon/788