Is there any custom event for error or submitting?

Hi @ultigendlemate

As for showing error message:

This modified code should also be showing message on submission fail:

<?php

function wpdocs_theme_name_scripts() {
	wp_enqueue_style( 'toastify-custom', 'https://cdn.jsdelivr.net/npm/toastify-js/src/toastify.min.css' );
	wp_enqueue_script( 'toastify-custom', 'https://cdn.jsdelivr.net/npm/toastify-js', '1.0.0', true );
}
add_action( 'wp_enqueue_scripts', 'wpdocs_theme_name_scripts' );

add_action( 'wp_footer', function(){ ?>
<script>
	(function($){
		$(function(){
			if( window.HUI ){
				var _popups = $(".hustle-popup");

				if( _popups.length ){
					_popups.on("hustle:module:submit:success", function(){
						handle_hustle_submission_event( $(this) );
					});
					_popups.on("hustle:module:submit:failed", function() {
						handle_hustle_submission_error_event( $(this) );
					});
				}
				function handle_hustle_submission_event( _element ){

					Toastify({
                        text: "This is a toast",
                        duration: 3000
                    }).showToast();

				}
				function handle_hustle_submission_error_event( _element ){

					Toastify({
                        text: "This is a toast",
                        duration: 3000
                    }).showToast();

				}				
				
			}
		});
	})(window.jQuery)
</script>
<?php }, 21 );

Note: this will only show predefined message; to intercept actual error you’d need some additional JS to read content of the error from the displayed error block, hide that block and pass the error to toast; this should be doable, I believe, but it would require more custom code and it’s out of the scope of our assistance, I’m afraid.

As for showing image:

The simplest way to show image would be to use “avatar” option key. You have these lines in the code:

Toastify({
	text: "This is a toast",
	duration: 3000
}).showToast();

so you can add “avatar” option like this

Toastify({
	text: "This is a toast",
	avatar: 'URL_OF_YOUR_IMAGE_FILE_HERE',
	duration: 3000
}).showToast();

Alternatively, you can instead add a custom class name and then simply use a regular CSS to style it (e.g. adding image as background, positioned accordingly):

Toastify({
	text: "This is a toast",
	className = 'toast-message',
	duration: 3000
}).showToast();

Or you can combine the two:

Toastify({
	text: "This is a toast",
	avatar: 'URL_OF_YOUR_IMAGE_FILE_HERE',
	className = 'toast-message',
	duration: 3000
}).showToast();

Best regards,
Adam