Can't figure out adding assemblies / operations to jobs created with the REST API

I’m trying to create a Quote, an RMA, a Sales Order, and Jobs in Epicor from a web app. All of these are already working well except the Job step, which seems more complicated than everything else combined.
It does create the job- and the part is on it ( because this is for RMAs, it’s a ‘Service Part’ that is not a real part but Epicor needs it to act like one ).

In the GUI, Actions > Job > Get Details will add operations and materials from the part.

In the API, there is a POST method at '/Erp.BO.JobEntrySvc/GetDetails that looks like it should do the same thing- but I can’t get it to affect the job at all.
It takes a lot of input fields, all of which are required, and some make no sense to me (particularly “sourceFile” and “sourceAltMethod”) so I might be doing it wrong.

{
  "currJobNum": "string",
  "currAsmSeq": 0,
  "sourceFile": "string",
  "sourceQuote": 0,
  "sourceLine": 0,
  "sourceJob": "string",
  "sourceAsm": 0,
  "sourcePart": "string",
  "sourceRev": "string",
  "sourceAltMethod": "string",
  "resequence": true,
  "useMethodForParts": true,
  "getCostsFromInv": true,
  "getCostsFromTemp": true
}

Is anyone successfully using the API to create and properly setup jobs? How many separate requests does it take to do it, and can it be done with only the same data I’m already using to make the RMA / quote / sales order?

I found this one too:
/Erp.BO.BomSearchSvc/GetDatasetForTree
That looks like I might have to call this with the part number, and then go through the returned data and individually add whatever materials and operations it came up with to the job?

have you tried using JobHead.UpdateEXT bo to create the entries for JobAssy? I believe I did that in the past with no major challenges.