SFMC Journey Builder Custom Activity Failed event without any error message

Question

I created a Custom Activity for SFMC Journey Builder and every time a contact reaches it a "Failed" event is logged and there isn't any more information than that.

I can see the execute call being made and the response is correct with the outArguments I set in the config.json file, see below:

{
  "workflowApiVersion": "1.1",
  "metaData": {
    "icon": "images/icon.png",
    "iconSmall": "images/icon.png",
    "category": "Ansira"
  },
  "type": "RESTDECISION",
  "lang": {
    "en-US": {
      "name": "Custom Activity",
      "description": "Custom Activity"
    }
  },
  "arguments": {
    "execute": {
      "inArguments": [],
      "outArguments": [
        {
          "message": "text"
        },
        {
          "response": "text"
        },
        {
          "payload": "text"
        },
        {
          "universeName": "text"
        },
        {
          "variationName": "text"
        }
      ],
      "url": ".../execute/",
      "verb": "POST",
      "body": "",
      "header": "",
      "format": "json",
      "timeout": 30000
    }
  },
  "configurationArguments": {
    "save": {
      "url": ".../save/",
      "body": "",
      "verb": "POST"
    },
    "publish": {
      "url": ".../publish/",
      "verb": "POST",
      "body": ""
    },
    "validate": {
      "url": ".../validate/",
      "verb": "POST",
      "body": ""
    },
    "stop": {
      "url": ".../stop/",
      "verb": "POST",
      "body": ""
    }
  },
  "wizardSteps": [
    {
      "label": "Step 1",
      "key": "step1"
    }
  ],
  "userInterfaces": {
    "configModal": {
      "height": 600,
      "width": 800,
      "fullscreen": false
    }
  },
  "schema": {
    "arguments": {
      "execute": {
        "inArguments": [],
        "outArguments": [
          {
            "message": {
              "dataType": "Text",
              "direction": "out",
              "access": "visible"
            },
            "response": {
              "dataType": "Text",
              "direction": "out",
              "access": "visible"
            },
            "payload": {
              "dataType": "Text",
              "direction": "out",
              "access": "visible"
            },
            "universeName": {
              "dataType": "Text",
              "direction": "out",
              "access": "visible"
            },
            "variationName": {
              "dataType": "Text",
              "direction": "out",
              "access": "visible"
            },
            "settings": {
              "dataType": "Text",
              "direction": "out",
              "access": "visible"
            }
          }
        ]
      }
    }
  },
  "outcomes": [
    {
      "arguments": {
        "branchResult": "success"
      },
      "metaData": {
        "label": "Success"
      }
    },
    {
      "arguments": {
        "branchResult": "error"
      },
      "metaData": {
        "label": "Error"
      }
    }
  ]
}

Sample response from the execute call:

{
  "branchResult": "success",
  "message": "Success",
  "payload": "payload",
  "response": "response",
  "settings": "settings",
  "universeName": "universeName",
  "variationName": "variationName"
}

Answer 1

After spending hours investigating, I found that the outArguments names have to be very short to be accepted.

So I changed my config.json file to have uniname instead of universeName and varname instead of variationName.

I also tried without uppercase letters (i.e. universename) but that still failed so it definitely is a length issue.

It would be helpful to have this kind of limitations in the documentation.