I have made a single entry visa to Korea, however not sure if I’m able to go to Jeju and back to Seoul. This is my travel plan moi.gov.qatar visa inquiry
Singapore fly to Seoul
Seoul fly to Incheon airport
Incheon airport take train to Gimpo
Gimpo fly to Jeju
And finally Jeju back to gimpo
I’ve seen a few stories for Chinese passport is that they used your visa in Jeju, resulting in not being able to return to Seoul as visa has been used. Hope to hear from you guys!