So, we've added a column to our Invoice Form.

It shows up in the print invoice form.

However, we are having problems adding the column to the sales/invoicing layout.

So here it is in our invoice form:

That column batch is what we added

Now in our layout where we enter invoices...we are unable to add the column (which is a secondary attribute ID)

It's not showing up in our list of columns to add:

Any ideas please as to what I'm missing? 

We would like to be able to add those batch numbers from the layout in inventory.