Selecting in States.StringToJson function - json

Question

It there is a way to process the result of States.StringToJson intesic function directly ? 
Currently in a step function, I try to handle the error from another synchronous step function call :
"OtherStepFunction": {
"Type": "Task",
"Resource": "arn:aws:states:::states:startExecution.sync:2",
"Parameters": {
"StateMachineArn": "otherstepFunctionCall",
"Input.$": "$"
},
"End": true,
"Catch": [
{
"ErrorEquals": [
"States.ALL"
],
"Comment": "OtherStepFunctionFailed",
"Next": "StatusStepFunctionFailed",
"ResultPath": "$.error"
}
]
},
All errors goes in a pass flow named StatusStepFunctionFailed, with the errors output in $.error path.
The $.error is composed of the error type and the cause as an escapedJson string.
"error": {
"Error": "States.TaskFailed",
"Cause": "{\"ExecutionArn\":\"otherfunctionarm:executionid\",\"Input\":\"foooooo\"}"
}
Is there any way to extract only the ExecutionARN from this input ? In my pass step, I convert the Cause path as a json, but i didn't find a way to select directly the ExectionARN part. The following :
"reason.$": "States.JsonMerge($.error.Cause).ExecutionArn"
return The value for the field 'reason.$' must be a valid JSONPath or a valid intrinsic function call (at /States/HandleResource/Iterator/States/StatusStepFunctionFailedHandleJSON/Parameters)
My current workaround is to use 2 pass flow, first convert the output and then formating.

Answer 1

I had a similar issue.
What I did was create a task to put the Cause into a new path parameter using StringToJSON. I put that task as the next from the error and then called the subsequent task from that one.
Using your variable names and values:
In the Catch, change the Next from StatusStepFunctionFailed to parseErrorCause
Then parseErrorCause is like this:
"parseErrorCause": {
"Type": "Pass",
"Parameters": {
"Result.$": "States.StringToJson($.error.Cause)"
},
"ResultPath": "$.parsedJSON",
"Next": "StatusStepFunctionFailed"
},
And StatusStepFunctionFailed accesses
"Variable": "$.parsedJSON.Result.Input",
to get foooooo