we have a requirement to auto populate the date signed field with the date and time stamp when the user has signed the document. Please let us know how do we do this using the REST API for creating and sending the Envelope. 

we see that there is a DateSigned tab on the API, but it requires us to provide a X and Y position of the date Signed field. We are not sure of the X and Y positions of the date signed field on each document which we send. Can you please let us know if there is anything better than this field to use