Hello, for all things related to Concur Web Services & API's, please reference the following links & videos:
API Developer Reference
Swagger API Explorer
SAP Concur Integrate Tools
Intro to SAP Concur Web Services
Integration Developers Guide
List Item API
I've studied API Developer Reference and one thing is not clear for me - is it any method to manage user role in workflow like Expense Approver, Authorized Approver, Cost Object Approver?