You cannot add a new source when editing/updating an answer.
https://wikirate.org/Research_Page?company=BP+plc.&metric=Global+Reporting+Initiative%2BDirect+greenhouse+gas+%28GHG%29+emissions+%28Scope+1%29+%28G4-EN15-a%29&view=edit&year=2018#
seems to be specific to answers with no sources (which we want to make impossible)
fixed.