If I'm understanding your issue correctly, you'd like to add a line item to a Line Item Subset--so that you can map list items to line items--but are having trouble adding the line item because it does not have a numeric data type.
You've come across a known limitation. A product manager would say it's working as intended.
The idea behind Line Item Subsets is that they enable you to turn a set of Line Items into a list so that you can then use the COLLECT() function to dimensionalize that data set in a downstream module and perform further calculations on it. For instance, in Module A you could have 10 line items applying to 3 dimensions, each showing some monthly metric or figure. But if you want the ability to show the YTD value for all 10 of those items, you can add all 10 of those Line Items to a Line Item Subset, add your original 3 dimensions (plus your Line Item Subset) to Module B, and then have a Line Item in Module B that calculated YTD for all 10 items in one fell swoop.
Because the intended use of Line Item Subsets is to support this COLLECT() functionality pulling forward numeric data, you're
Can you elaborate on the mapping you're attempting to do?
For our other manufacturing customers we'll typically have a mapping of Lots to Factories, indicating the Factory where a Lot (or grouping of Lots) will be produced.
From the screenshots it looks like you may be doing something different here
What's the next step after you capture / populate (manually or formulaically) this mapping in the module? Are you using it for some aggregation, calculation, or transformation of data?
First of all, I like the creativity. Creating Line Item Subsets and using them in mappings can be a clever solution to address nuanced functional requirements or user experience requirements that come up every now and then.
Happy to continue the conversation and figure out the best approach with you, but based on the information provided thus far, you may have more luck by making a list containing your Lots, and having that line item be of data format type "List" as opposed to "Line Item" or text.
This way you can, for each Factory, assign a Lot item, looking it up from a property or line item that applies to the Factory Inbound Load list.
Let me know your thoughts, also happy to hop on the phone to discuss.