Problems with access to the Restfull API via oAuth

Dear Support Forum members,

I try to access the Woocommerce API with vb.net and oAuth.
I tested the code from this site:
https://frank-it-beratung.com/blog/2010/11/11/twitter-api-mit-oauth-und-visual-basic/
With this code i get an 500 error.

Then i was trying to access the API with Restclient and following site:
https://term.ie/oauth/example/client.php

With this two tries, i get the error 401.

If i access the server https://term.ie/oauth/example/request_token.php eith the key “key” and the secret “secret”,
it work without any problem (feedbackcode is 200).

Wordpress is 4.7.4 and Coocommerce is 3.0.6.

What should i do?