parsing upload session finish error

You should only upload one chunkLength's worth of data with each call. The following line seems to indicate that you're uploading much more than that for each though:

range = NSMakeRange(Int(startPosition), (data.length)-Int(startPosition))

I.e., the end of the range should probably be something like startPosition + chunkLength.

Anyway, each of the three calls have the ability to take a chunk of data, but it's not required that you do supply data to each. You just need to make sure you upload all of the chunks in order.

Also, it looks like you're still not checking the response on uploadSessionAppend. You should implement the .response callback on that just like the other calls.