Value null at 'stateMachineArn' failed to satisfy constraint: Member must not be null

Question

I followed AWS Step Functions and added the AWS Step Functions.

But when I used the code below to try to call the Step Functions,

import { ajax } from 'rxjs/ajax';

// ...
ajax.post(
  url,
  {
    input: JSON.stringify({
      formId: action.payload.formId,
      fields: action.payload.fields,
    }),
  },
  { 'Content-Type': 'application/json' },
).pipe(
  map(res => actions.sendRequestSucceed(res)),
  catchError(actions.sendRequestFailed),
)

It returns the error:

response: {
    message: "1 validation error detected: Value null at 'stateMachineArn' failed to satisfy constraint: Member must not be null"
    __type: "com.amazon.coral.validate#ValidationException"
}

Answer 1

Took me a while to figure out.

First need set up API Gateway, you can follow this tutorial.

Note the Action is StartExecution.

Here is StartExecution API document.

{
   "input": "string",
   "name": "string", (Optional)
   "stateMachineArn": "string"
}

After adding stateMachineArn which can be found at in your Step Functions -> State machines

in the code

ajax.post(
  url,
  {
    input: JSON.stringify({
      formId: action.payload.formId,
      fields: action.payload.fields,
    }),
    stateMachineArn: 'arn:aws:states:us-west-2:000000000000:stateMachine:SendFormStateMachine',
  },
  // ...

Then it works.

Also note StartExecution input only accept string. If you need pass an object, you can use JSON.stringify.