Whilst working on bug #41592 I was tempted to impliment a new refunds api and utilise it in that bug but I decided it would be better off on it's own bug, so here that is. We should add support for creating refund directly via the API's.. I intend to expose all the accounts, registers and point of sale functionality via API's in the coming weeks and eventually re-write the POS pages in Vue... this is the first step.