It should be one user per field.
I’m trying to assign a pre-defined promotion code to users when their account is created. The accounts are being created from the frontend (successfully) after a payment from Stripe is made. So my client enters promotion codes in the structure field and leaves the user field blank. A user then signs up, and in a user.creater:after hook I check for the next code in the structure field that has an empty user field and write that user to the structure field. I was trying to repurpose this code to do that: Update specific structure field - #2 by texnixe