right now pending is not supported right now and than has a code like something with 1XXXX. BUT not right now - we will do that later this year.
Till now you'll get only 20000 if ok or 4XXXX/5XXXX for errors (have a look at the response codes https://www.paymill.com/de-de/dokumentation/referenz/api-referenz/#response-codes).
If you need some other codes you want to try than please use one of the creditcardnumbers displayed at the testing page at docu https://www.paymill.com/en-gb/documentation-3/reference/testing/ .
Best, Christian