BSEG-PERNR is not being populated despite LFB1-PERNR being populated

I have populated the vendor master with the personnel number

However when I post a document to accounts payable this field is not populated in either the vendor nor the GL line item in BSEG.

we do not have SAP HR so there is no integration.

I have set the field of personnel number as optional in the control of the AP reconciliation account and in the GL account.