Automatically post the new form submissions stored in the google sheet (Integrated) to slack

Question

I have a custom form which is automatically storing the new submissions to a google sheet. Since the form is not a google form, OnFormSubmit event trigger is not working. Is there any other way to make the event trigger as soon as a new row is added to the google sheet, which will be posting the message on slack with the details.

This is the code I have right now for the trigger and it's not working because the form is not a google form. ​

ScriptApp.newTrigger("submitValuesToSlack")
    .forSpreadsheet(SpreadsheetApp.getActiveSpreadsheet())
    .onFormSubmit()
    .create();
}

Since it is using AppsScript, onEdit is also not working on it to trigger the event. Any help or suggestions are appreciated, and FYI I cannot move to google forms. Thank you.