@Ankur Bawiskarokay, Can you help me with the DOM manipulation. Let's give a try

Thanks

@is_12 

link shared by @palanikumar should help, you should enhance it as per your logic in catalog client script

Ensure you detect the correct HTML element

If my response helped please mark it correct and close the thread so that it benefits future readers.

You should update the logic in a way that form gets submitted only if the response is true. You can use this code

function onSubmit() {
    if (g_user.hasRole('sn_customerservice_agent')) {
        var ga = new GlideAjax('catalogUtils');
        ga.addParam('sysparm_name', 'hasExistingRITM');
        ga.addParam('sysparm_account', g_form.getValue('account'));
        ga.addParam('sysparm_userId', g_form.getValue('contact_name'));
        ga.addParam('sysparm_catalogItem', g_form.getUniqueValue());
        ga.getXMLAnswer(setData);
        return false; // Cancel the form submission
    }
}
function setData(response) {
    var answer = response;
    alert('reponse' + answer);
    if (answer == 'false') {
        alert(getMessage('You are not allowed to order as there is an existing request for this customer'));
    } else {
        alert("else if alert");
        g_form_submit(); // Submit the form only if the response is true
    }
}

@palanikumar I need to disable the button order now button

Thanks,