goto property of server response is optional.

Use this response to goto a step or sub flow:

{
"version": "v1",
"content": {
"goto": "SOMETHING"
}
}

You can goto:

Goto | SOMETHING = | e.g.

A step | step name (unique) | Welcome

A step | node_ns | f244n7831

A sub flow | sub_flow_ns | f244s1032

Find a sub flow and follow steps 1 and 2 in the following screenshot:

Select a step, click "Copy Ref Url for this step", paste somewhere, then you will see the node_ns of this step: