Steps to Change product's Alternate Lookup:
1) On the management console, navigate to the 'Products' page
2) Locate the desired product, click the 'pencil' icon to it's right
. . . .
3) You are taken to the 'Product Details' page. Ensure the blue 'Alternate Lookup' box to the left is checked, to view that setting on the right.
4) On the right-hand side of the page, scroll down to find the 'Alternate Lookup' box. Enter a value here if desired, or leave it blank to automatically use product ID instead.
For this example, we see that the 'Alternate lookup' matches the product barcode, thus that number is used for "menu_item_id" in the above JSON data.
5) Click 'Save' on the top-right
6) Refresh all POS stations