When I use DOI to add references, JabRef displays “unresponsive” or “connection error”. When I manually add an entry and paste the DOI, clicking on the yellow box can connect to the IEEE interface, but clicking on the red box button displays “DOI not found”, and still unable to automatically add reference information. I hope someone could kindly explain. Thank you so much!
You might wanna try the third button in the DOI row, which is called Get bibliographic data from DOI.
I think the difference between Lookup DOI and the Get bibliographic data from DOI button is that the former requires you to have bibliographic data like author, title, publisher, etc. and JabRef will then try to find the correct DOI and fetch bibliographic data based on that DOI, whereas the latter, requires you to have a DOI and nothing else and JabRef will then query bibliographic data. Looks like this is not well enough documented: Complete information using online databases - JabRef.