HttpRequest FileUpload Error in C# - but works via Postman

Dear Community,
I tried uploading a file through Postman UI, which works very well.
However, it’s equivalent C# HttpRequest based code gives a “Badrequest” error (invalid value - File)

Postman Console shows the value: “Undefined” for “File”, which doesn’t tell enough about the Type / Encoding that needs to be used here.

Is there a way to see the value for “File” that is sent with the request?
Appreciate any help. Thanks in advance.

Kind regards,