How to kick Adobe workflow->document -agreement from C Sharp

I have an adobe personal account. I created a document template in shared library which needs to populate customer details from database, so I created form fields. And also I created a workflow- will first send this document to the customer for signature then approver for approving the document. I need to kick this workflow using RESTAPI in C#. I created access key from Postman and try to call the url thru RestClient and pass the key in header. Its always saying Invalid token or expired. I also need to kick this workflow and pass required field values using agreement.mergeFieldInfo. Is there any sample code, how to connect from .NET to my personal account and kick my workflow.