Form Field Validation non-active if fields are hidden

I have created a custom form which is part of an application process and in this form I have a menu field with two options which are: 'SIngle payment' or 'Split payment'. If split payment is selected then it reveals other form fields. I have done this with this small piece of Javascript:

<script>
$('#payment_option').on('change',function(){
if( $(this).val()==="Split"){
$("#split-payment").show()
}
else{
$("#split-payment").hide()
}
});
</script>

if the 'Single Payment' option is selected then the additional form fields are hidden.
Consequently is there a way I can have validation for these fields but only effective when the form fields are visible

I hope this makes sense!

use server validation for those fields, you will then need to edit the server validation for those fields and add an if statement:

if(isset($_POST['menuFieldName']) && $_POST['menuFieldName'] == "Split") {
<validation for the other fileds>
}

If I use the CSS form builder to create the form before adding my "show/hide javascript function". does that mean I should have the required option ticked in the 'Edit Field Values' window?

yes, that is correct.

if you need help setting this up, we can help in a premiere support appointment:
http://www.webassist.com/premier_request.php

Thanks Jason, ill see how I get on. If I fail then I will get back to you!

Probably the later!!

are you able to explain in more detail where I add the if statement? I am clicking on the WA Server Validations behaviour in the Server Behaviours Window. So do add it here or do I have to adjust the code manually?

you have to adjust the code manually.

in the code for the server validation, locate the lines that validate the conditional items, and add an if statement around them.