I have been building a dashboard in retool to send a message to multiple selected users, but since slack api (https://slack.com/api/chat.postMessage) used to send message to a single user.

I have tried to trigger the API through JSQuery as mentioned below:

async function slackTrigger(array) {
  for (const value of array) {
    await send_slack_message.trigger({
      additionalScope: {
        channel: value  
      },...

But encountered with this error:

"ok": false,
  "error": "invalid_arguments",
  "warning": "missing_charset",
  "response_metadata": {
    "messages": [
      "[ERROR] missing required field: channel"
    ],
    "warnings": [
      "missing_charset"
    ]
  }
}