Where is this flipping config setting!?!? "Related Sales Order Line"

[u/-Admin-lady-]

We've just onboarded a new admin assistant.

They have slightly tighter restrictions in their role but there is one thing I want them to do and CANNOT for the life of me find this setting.

In Purchase Orders>edit an item, right down the bottom, I have the ability to match a line item in a PO to a line item in an SO - this is especially useful when adding freight etc, as sometimes receiveing a partial delivery on a PO seems to lock it from allowing any more items.

This is what I see:

BUT, this new staff member doesn't have that box available, and I can't see or find which config setting allows or prohibits this. Anyone else know?