@tylerlamparter Yes "salesorder" is the value for celigo_nlobjTransformType. I just fixed this issue by removing Internal ID from mapping. Now receiving new error:
{ "code": "VALID_LINE_ITEM_REQD", "message": "You must have at least one valid line item for this transaction." }
Here is an article that discusses creating a NetSuite record with a subrecord mapping similar to what you are trying to do, have you read through this by chance? It may help you as there are detailed screenshots of an item fulfillment record with inventory details.
@bhargavmashru I was able to get this on SS2.X with these mappings. Your mappings will be a little different since you have lots, but shouldn't be too far off. I did take out the use dynamic mode mapping.