The format of the request and the response changed when we moved to a strongly typed model.
API 1.1 code needs some reworking to use API 2.x.
The good news is that the model of API 2.s is not bound to change any time soon and that API 1.1 is still fully maintained. No new features are added, but it is not going away any time soon.
The recommendation is to use API 2.0 for the new versions of your applications, just phasing out the usage of API 1.1
HTH
--Alessandro