Tyk Cloud: How to retrieve values/parameters?

Direct calls at the endpoint works well. The three possible direct calls on the endpoint provide the desired data:
https://www.myurl.com/API/
https://www.myurl.com/API/itemA/
https://www.myurl.com/API/itemA/2017-11-01

I would like to use API-Gateway from tyk, but tyk is only retrieving the base url. When I make a call on
https://myname.cloud.tyk.io/productname/itemA, then I want that tyk retrieves data from https://www.myurl.com/API/itemA/, but I get only the data from base url.

How to pass the values correctly in tyk Cloud? When you say that my rewrite isn’t firing, then can give me advise how to do that with tyk? In tyk cloud, I’ve seen that there is a tab to rewrite url, but I don’t understand how to use it, because the docu is insufficient.