Add a Gravity Forms validation filter to check default values

functions.php

<?php
// Append the Gravity Forms ID to the end of the filter so that the validation only runs on this form
add_filter('gform_validation_1', 'custom_validation');
function custom_validation($validation_result){
    $form = $validation_result["form"];
    foreach($form['fields'] as &$field){
        /* Check that the value of the field that was submitted. e.g. the name="input_1" that is generated by Gravity Forms */
        if($_POST['input_1'] == "Your First Name"){
         // set the form validation to false
         $validation_result["is_valid"] = false;
            //The field ID can be found by hovering over the field in the backend of WordPress
             if($field["id"] == "1"){
                 $field["failed_validation"] = true;
                 $field["validation_message"] = "This field needs to be your actual first name.";
             }
         }
    if ($_POST['input_2'] == "Company Name"){
        // set the form validation to false
        $validation_result["is_valid"] = false;
        //The field ID can be found by hovering over the field in the backend of WordPress
                if($field["id"] == "2"){
                    $field["failed_validation"] = true;
                    $field["validation_message"] = "This field needs to be your company name";
                }
            }
        }
    //Assign modified $form object back to the validation result
    $validation_result["form"] = $form;
    return $validation_result;
}?>