gravity_forms_validation.php

<?php
//This is a filter to change the default validation message that Gravity Forms generates
add_filter('gform_validation_message', 'change_validation_message', 10, 2);
function change_validation_message($message, $form)
{
    return "<div class='validation_error'><strong>Oops!</strong> Looks like there’s something wrong. Please review the form above.</div>";
}

// Often forms in Gravity Forms to need to start with default values and we need to check the form in case the user hasn't entered new data and give them a validation message back

// Append the Gravity Forms ID to the end of the filter so that the validation only runs on this form. In this example I'm doing it on Form #2
add_filter('gform_validation_2', 'custom_validation');
function custom_validation($validation_result)
{
    $form = $validation_result["form"];
    //We need to loop through all the form fields to check if the value matches and of the default values
    foreach ($form['fields'] as &$field) {
        //Check if the value is equal to the Default Value you entered in Gravity Forms
        if ($field["value"] === "Your 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;
                $field["validation_message"] = "Please enter your name.";
            }
        }
        if ($field["value"] === "Job Title") {
            // 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"] == "4") {
                $field["failed_validation"] = true;
                $field["validation_message"] = "Please enter your job title.";
            }
        }
        if ($field["value"] === "Contact phone number") {
            // 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"] == "5") {
                $field["failed_validation"] = true;
                $field["validation_message"] = "Please enter your contact phone number.";
            }
        }
        if ($field["value"] === "Company") {
            // 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"] == "6") {
                $field["failed_validation"] = true;
                $field["validation_message"] = "Please enter your company name.";
            }
        }
    }
    //Assign modified $form object back to the validation result
    $validation_result["form"] = $form;
    return $validation_result;
}?>