Str.join is not a function

Hey there,
I’m new to n8n community and am having a hard time setting up a basic workflow between Typeform and Slack.

{
  "name": "Test",
  "nodes": [
    {
      "parameters": {},
      "name": "Start",
      "type": "n8n-nodes-base.start",
      "typeVersion": 1,
      "position": [
        0,
        50
      ]
    },
    {
      "parameters": {
        "formId": "aQWcfa"
      },
      "name": "Typeform Trigger",
      "type": "n8n-nodes-base.typeformTrigger",
      "typeVersion": 1,
      "position": [
        60,
        -150
      ],
      "webhookId": "5d7690a7-ba10-4bdd-a43a-34c9def8e745",
      "credentials": {
        "typeformApi": "Typeform"
      }
    },
    {
      "parameters": {
        "resource": "channel",
        "channelId": "={{$node[\"Typeform Trigger\"].json[\"Nom de la room slack\"]}}",
        "additionalFields": {}
      },
      "name": "Slack",
      "type": "n8n-nodes-base.slack",
      "typeVersion": 1,
      "position": [
        350,
        -130
      ],
      "credentials": {
        "slackApi": "Slack GR"
      }
    },
    {
      "parameters": {
        "authentication": "oAuth2",
        "resource": "channel",
        "operation": "invite",
        "channelId": "={{$node[\"Function\"].json[\"myVariable\"]}}",
        "userIds": "UK5GD8R3P"
      },
      "name": "Slack1",
      "type": "n8n-nodes-base.slack",
      "typeVersion": 1,
      "position": [
        940,
        -110
      ],
      "credentials": {
        "slackOAuth2Api": "GR-slack"
      }
    },
    {
      "parameters": {
        "functionCode": "items[0].json.myVariable = items[0].json.id;\nreturn items;"
      },
      "name": "Function",
      "type": "n8n-nodes-base.function",
      "typeVersion": 1,
      "position": [
        600,
        -120
      ]
    }
  ],
  "connections": {
    "Typeform Trigger": {
      "main": [
        [
          {
            "node": "Slack",
            "type": "main",
            "index": 0
          }
        ]
      ]
    },
    "Slack": {
      "main": [
        [
          {
            "node": "Function",
            "type": "main",
            "index": 0
          }
        ]
      ]
    },
    "Function": {
      "main": [
        [
          {
            "node": "Slack1",
            "type": "main",
            "index": 0
          }
        ]
      ]
    }
  },
  "active": true,
  "settings": {},
  "id": "1"
}

When i try to execute the last node it sends me :slight_smile:
TypeError: this.getNodeParameter(...).join is not a function at Object.execute (/usr/local/lib/node_modules/n8n/node_modules/n8n-nodes-base/dist/nodes/Slack/Slack.node.js:279:73) at Workflow.runNode (/usr/local/lib/node_modules/n8n/node_modules/n8n-workflow/dist/src/Workflow.js:492:37) at /usr/local/lib/node_modules/n8n/node_modules/n8n-core/dist/src/WorkflowExecute.js:395:62
Any help would be greatly appreciated !
Thanks in advance,
Nicolas

Welcome to the community @Nicolas_Monnier!

The parameter “User IDs” is set to an invalid value. It should be an array of strings but in your case it is somehow only a string. That breaks then the node.

How did it get set to that value? That should not be possible via the UI.

If you recreate the node and then set the values again via the UI it should work fine.