[API-users] API for batch calling GBIF id -> checklist ID

Hi I have a large number of GBIF ids (~ 2 million), for which I wish to know any existing International Plant Names Index IDs (IPNI s). What’s the easiest way to do this? I can use the standard API, e.g. http://api.gbif.org/v1/species/2705290/related for 2705290 = Avena sativa, which gives me an output that contains several IPNIs (in this case, 164949-3, 391732-1, 27200-2, of which the number 391732-1 seems to be the canonical one, although I can’t figure out how to identify it as such from the GBIF API output) It will obviously be tedious (and unwarranted) to make 2 million API calls. What’s the recommended way to do this? Yan