Complete Form

FORM UI

<form action="<?php echo esc_url( admin_url('admin-post.php') ); ?>" method="post">
    <input type="hidden" name="action" value="contact_form_submission">
    <?php wp_nonce_field( 'contact_form_action', 'contact_form_nonce' ); ?>
    <input type="text" name="name" id="name" >
    <input type="email" name="email" id="email" >
    <input type="submit" value="Submit">
    <div class="g-recaptcha" data-sitekey="RECAPTCHA_SITE_KEY"></div>
    <input type="submit" value="Submit">
</form>

FORM Handler

<?php
/**
* Handle form submission.
*/

add_action( 'admin_post_nopriv_contact_form_submission', 'handle_contact_form_submission' );
add_action( 'admin_post_contact_form_submission', 'handle_contact_form_submission' );

function handle_contact_form_submission() {
    // Check if the nonce is set.
    if ( isset( $_POST['contact_form_nonce'] ) && wp_verify_nonce( $_POST['contact_form_nonce'], 'contact_form_action' ) ) {

        // Check if the name is set.
        if ( isset( $_POST['name'] ) ) {
            $name = sanitize_text_field( $_POST['name'] );
        }

        // Check if the email is set.
        if ( isset( $_POST['email'] ) ) {
            $email = sanitize_email( $_POST['email'] );
        }

        // Check if the name and email is set.
        if ( isset( $name ) && isset( $email ) ) {

            // Validate Google reCAPTCHA
            $recaptcha_response = $_POST['g-recaptcha-response'];
            $recaptcha_secret = 'YOUR_RECAPTCHA_SECRET_KEY';
            $recaptcha_verify = wp_safe_remote_get("https://www.google.com/recaptcha/api/siteverify?secret=6LezqOMnAAAAAFLcXYKpO0KKnhhvybmh1l-ZmGez&response=$recaptcha_response");
            $recaptcha_data = json_decode($recaptcha_verify['body']);

            if ($recaptcha_data->success) {
                // CAPTCHA validation passed
                // Handle file upload if needed

                // Send email or save data to database

            wp_safe_redirect($_SERVER['HTTP_REFERER']);
            } else {
                // CAPTCHA validation failed
                echo "reCAPTCHA verification failed. Please try again.";
            }
        }
        else{
            wp_safe_redirect($_SERVER['HTTP_REFERER']);
            echo "Please fill all the required fields.";
        }


    }
}