It will depend on your programming environment – different libraries make it easier or harder to capture the raw HTTP of the request in action.
So now you have an example that functions for you with your own keys – if you use the same exact timestamp, nonce, and keys for the successful request in your code, you should be able to build a request that looks exactly the same. Once you can reproduce the exact same request, then try it with a recent timestamp and a new nonce.
Make sure that you’re not sending authorization in multiple ways (mixing query string and auth headers for example).