miniShop2.Message = {
success = function(message){
    IziToast.show({message: message});
}
}

Ну а на fenom всё выглядит намного проще:

$(document).ready(function() {  
    miniShop2.Callbacks.Order.submit.response.success = function (response) { 
if (response.data['redirect']) {
                    document.location.href = response.data['redirect'];
                } else if (response.data['msorder']) {
                    if(document.location.pathname.indexOf('checkout') == -1){
                        document.location.href = document.location.origin + '/getorder.html'
                            + (document.location.search ? document.location.search + '&' : '?')
                            + 'msorder=' + response.data['msorder'];
                    }
                    else{
                        document.location.href = document.location.origin + document.location.pathname
                            + (document.location.search ? document.location.search + '&' : '?')
                            + 'msorder=' + response.data['msorder'];
                    }
                } else {
                    location.reload();
}
	}; 

    });

miniShop2.Callbacks.Order.submit.response.success = function (response) { alert('eeeeeeee'); };

miniShop2.Callbacks.Order.submit.response.error = function(response) { }