How to implement Batch request for BULK Insert/Update using Web Api in Console app for dynamics 365.

We are implementing Batch request for Bulk Insert using Web Api request in console app , but getting error while Post execution request as 'This operation is not supported for a relative URI'  , Same Batch request we already implemented in JavaScript and also tested in Postman, its works fine. Can anyone knows the correct implementation of Bulk Insert Batch request in C#.