target-unknown-step

[wizzard] unknown target "<id>". A transition leads to a key of steps, or to @end from on.next.
Correct the id, or add the step it names. …/errors/target-unknown-step

Returned by validateFlow, once per transition, with path ending in on.next or on.back, and listed in the message of flow-invalid by assertFlow.

A transition names the step it leads to, as a string or as the to of { to, when }. That id has to be a key of the steps beside it - in an inline sub-flow, a step of that sub-flow, not of the root; on.next may also name @end, the exit. A navigation that took this transition would have nowhere to go. The usual causes are a typo and a step renamed without its transitions.

{
  "steps": {
    "payment": { "on": { "next": "confirm" } },
    "confirm": {}
  }
}

Correct the id, add the step it names, or use @end if the transition was meant to finish the flow. Transitions are described in the flow guide.