Integrator.io Item Fulfillment creations always fail for "Failed to create, update/transform record because You have attempted an invalid sublist or line item operation." If I remove the line item mappings, the entire order will fulfill. I've mapped the SKU to Item ID, Internal Item ID, Sales Order Line ID, and all with and without 'Use as a key field to find existing lines'. I am at a loss. Item receipts work without issue, but item fulfillments are giving me grey hairs.

A few thoughts: Do either of the fields have a hierarchy e.g. parent : child Is the location binned, if so you may need an inventory detail record. Do any of the quantities exceed the quantity on the SO? Can you create the IF through the Netsuite UI? What mandatory fields are there? Lastly - you could try hardcoding in the item internal ID as a test and seeing if that works?

Both have parents. Neither are binned/lot/serial. Quantities do not exceed. Can be created through SO. Nothing required on the form outside the norm (date/status/an item with qty and fulfilled checked).