main.js

      success: function(response) {
        
        // added portion starts here
        let requredResponse = response.slice(response.length - 12);
        // added portion ends here
        
        if (requredResponse == "Message sent") { // change response to required response
          $(".form-message").html(
            "Your message has been submitted successfully"
          );
          $(".form-message").css("color", "lightgreen");
          $(".form-message").css("opacity", "1");
          $(".form-message").show();
          $(".form-message")
            .delay(5000)
            .fadeTo(1000, 0);
          $("#form").each(function() {
            this.reset();
          });
        } else {
          $(".form-message").html("Oops. Something went wrong.");
          $(".form-message").css("color", "#ff9494");
          $(".form-message").css("opacity", "1");
          $(".form-message").show();
          $(".form-message")
            .delay(5000)
            .fadeTo(1000, 0);
          $("#form").each(function() {
            this.reset();
          });
        }
      }