Step/section 4C on Exercise 1 instructs you to use api/core/items/[uuid]/bitstreams, but it looks like you need to get the bundle uuid and pull the bitstreams using /api/core/bundles/[uuid]/bitstreams to get bitstreams.
Also, possibly not important, but the current HAL browser tool starts at "/server/" and all the instructions for the tutorial start at "/api/".
I'm just working my way through. I very much appreciate the tutorial. Thank you, all!