Custom fields have a backend ID that is displayed in the API.
You will need to find the ID and match it to the field within the API call here:
https://apidocs.hibob.com/reference/get_company-people-fields
It will display the ID and the field name for example:
"id": "root.custom.field_1680790722854",
"category": "root",
"name": "HRBP",
"description": null,
"jsonPath": "custom.field_1680790722854",
"type": "employee-reference",
"typeData": {},
"historical": false