17. In the step's Pre-Expression add this: Step.AsPropertyObject().SetValString("Result.UID", PropOption_InsertElement, "12345")
I had a typo in Step 17, it should be:
17. In the step's Pre-Expression add this: Step.AsPropertyObject().SetValString("Result.UID", PropOption_InsertIfMissing, "12345")
PropOption_InsertIfMissing instead of PropOption_InsertElement. Funny thing is, those options have the same constant value of 1, which is why when I tested, I didn't get any errors.