Position Extraction - Sample REST JSON/PDF

Hi I have a working sample with Document Extraction using the eSignlive signature Field in [] and I'm converting it to using Position Extraction , using regular Field Name in the PDF and using the same JSON payload. However, I cannot get the ESL to recognize the Signature Fields under Position Extraction . do you have an example of using Position Extraction with REST? Or point out the main key attributes which is responsible in defining the SIgnature Controls for the Roles in the JSON?