How to model a wizard-like sequential process in REST?

How to model a wizard-like sequential process in REST?

Each step is long and async, each step needs new client input based on results from previous step. Most of the samples I found only involves adding a new element to a collection and then modifying the element so I don't know how to apply to my case.

If I try to make an analogy to the process, it will be like this:

Client submit mystery package

Server slowly unpacks it

　It's cake! Client input how many slices to cut

　　Server cut cake slowly

　　　Client get sliced cake

　It's bomb! Client input whether to cut green line or red line

　　Server disarm bomb slowly

　　　Client get disarmed bomb

Unpacking, cutting, disarming are async sequential singular action with singular output, the samples apply to multiple elements in a collection so it feels weird when I try to model these singular actions...

Thanks.