Invalid Authorization header to obtain authorization token

Unable to obtain the authorization code using getting the below errror

trying mimic the documentation to obtain the authorization token
POST /oauth2/token HTTP/1.1

grant_type=authorization_code&
code=authorization-code&
client_id=your-client-id&
client_secret=your-client-secret&
redirect_uri=application-redirect-uri
request you to help what we are missing here and guide .