Message not sent to discord webhook when called by onEdit function

I am trying to use the discord webhook with google sheets.

Here is the function to send a message to discord given a webhook url. This function works perfectly fine when called manually (not inside onEdit).

function sendDiscord(msg) {
  var url = ""; // webhook url

  var message = JSON.stringify({
      content: msg
  });

  var options = {
    'method': 'post',
    'payload': message,
    muteHttpExceptions : true,
    contentType: "application/json"
  };

  var res = UrlFetchApp.fetch(url, options);
}

Input: https://i.gyazo.com/cf8686a85a1e281de64c44ea491f75ff.mp4

Output:

But whenever I try to call the same function inside onEdit, the message does not pop up on discord.

function onEdit(e) {
  var ss = SpreadsheetApp.getActiveSpreadsheet();

  var tSheet = ss.getSheetByName("Tracking");

  if (e.range.getColumn() === 3) {
    if (e.value === "Needs Response") {
      tSheet.getRange(e.range.getRow(), 1, 1, tSheet.getLastColumn()).setBorder(true, true, true, true, false, false, "red", SpreadsheetApp.BorderStyle.DOUBLE);
      sendDiscord("The status has been updated."); // why does this line not run ???
    }
    else if (e.value === "To Be Sent") {
      tSheet.getRange(e.range.getRow(), 1, 1, tSheet.getLastColumn()).setBorder(true, true, true, true, false, false, "red", SpreadsheetApp.BorderStyle.DOUBLE);
    }
    else {
      // remove border
      tSheet.getRange(e.range.getRow(), 1, 1, tSheet.getLastColumn()).setBorder(false, false, false, false, false, false, null, null);
    }

  }

}

Everything else in the onEdit() function works perfectly fine as well. As you can see, when I selected "Needs Response" on google sheets, it added the borders, but did not send the message to discord.

Execution log running a test function by pressing "Run" using the same line:

function test() {
  sendDiscord("The status has been updated.");
}

Log: 5:01:39 PM Info

Following Ruben's suggestions, here is what I am seeing in the "My Executions" tab:

Exception: You do not have permission to call UrlFetchApp.fetch. Required permissions: https://www.googleapis.com/auth/script.external_request at sendDiscord(Code:18:25) at onEdit(Code:34:7)