<?php
add_filter('cred_form_validate','chr_validation',10,2);
function chr_validation($error_fields, $form_data)
{
    //field data are field values and errors
    list($fields,$errors)=$error_fields;
    //uncomment this if you want to print the field values
    //print_r($fields);
    //validate if specific form
    if ($form_data['id'] == FORMID)
    {
       
        //check my_field value
        if ($fields['generic-field']['value'] != types_render_field("custom-field", array()) )
        {
            //set error message for my_field
            $errors['generic-field'] = 'Please enter a correct PIN.';
        }
    }
    //return result
    return array($fields,$errors);
}