Create a custom field option. If the sort key is not supplied, it’ll default to 1000, so the option appears near the end of the list.
Created response.
{
"custom_field_id": "01FCNDV6P870EA6S7TK1DSYDG0",
"id": "01FCNDV6P870EA6S7TK1DSYDG0",
"sort_key": 10,
"value": "Product"
}