Hi Erno,

Thank you for your interest in our plugin.

Can you please explain to me what do you mean by "with Amelia can we add custom fields along the with booking such as GCLID & UTM parameters"? This cannot be created as a custom field but there is another way.

What you can do is to set Redirect URL in General settings of plugin, so when customers come to that Congratulations page it will be shown Finish button, so when they click on it, it will be redirected on your custom URL which you define (so you can use it on tracks). 

Also, you can use hooks like beforeConfirmedBooking that will be triggered when your customers confirm booking. You can set that redirect URL that you need like on this script (we use https://www.google.com as example, but you will replace this with your own URL)

<script>
window.beforeConfirmedBooking = function()
{
window.location.href = "https://www.google.com";
};
</script>

Please insert this script on page where you insert Amelia shortcode.

Best regards.