The GET /api/v2/conversations/calls resource only returns active calls for the session's user. If you don't have any calls connected to that user, you won't get any results.
To get queue calls, you'll need to use the conversation detail query using the resource POST /api/v2/analytics/conversations/details/query. This will return both historical and current data, so you'll need to filter the query and/or results appropriately to get on the data you're interested in.
I tried to change my routing state from Idle to Available through PureCloud menu, but I was immediately kicked out the queue.
This is expected. You changed your presence from On Queue to a presence that is not On Queue (literally any other presence). More information about routing and presences can be found on the resource center. The article on Agent availability will be a good place to begin.
Sorry,I just want to ask how did step2 happen?
when I go step3 it`s return "Can only change status from NOT RESPONDING to IDLE",
so can you tell me how to change status from OFF_QUEUE to NOT RESPONDING?
Thank you very much!
See the article Understanding Presence. There's a section at the bottom about ACD Routing Status that explains what to expect from and how to use the routing status.