"Assign Legal Number" Checkbox on AR PRint

I’m trying to work a support case with Epicor on the new Kinetic forms.
On version 10.2.200 the “Assign Legal Number” box is automatically checked when we go to print an AR form and this is the behavior we want.
Kinetic does not do this and the box is read only.
Yes–I do know that you can go to Actions > Legal Numbers > Assign Legal Number, but the case was opened because the Kinetic behavior is different.

The problem support is having is they cannot figure out how to get that checkbox in the classic window to be checked or even editable, so the tech cannot submit to development because he doesn’t have replication steps.
I have no clue how legal numbers work and don’t know the requirements to get that box to be editable. Does anyone know the complete setup? The tech created an AR legal number and also checked the box in the Company Config > Legal Numbers called “Require For AR Invoices and Credit Memos”, but this does not allow that box to be checked. What’s missing? Anyone know? Is this, perhaps, a Mexico CSF thing?