I could be wrong, but I don't think Vueling sell the route as a BA or EI codeshare. It is a missed opportunity for IAG to cross market, as there must be lots of people who use the Belfast airports who book via the British Airways or Aer Lingus apps. IAG don't seem to be that great at joined up marketing, as it is only very recently that the Aer Lingus flights form BHD to EDI and MAN have become available to book under a BA code on the British Airways app.