Code-Snippets-Functions/Execute a function on a child site/WooCommerce/characters-only-validation-first-name-last-name.txt

add_action( 'woocommerce_after_checkout_validation', 'bks_validate_fname_lname', 10, 2);

function bks_validate_fname_lname( $fields, $errors ){
    if (!preg_match( '/^[a-zA-Z ]+$/', $fields[ 'billing_first_name' ])){
        $errors->add( 'validation', 'First name should only have no special characters.' );
    }
    if (!preg_match( '/^[a-zA-Z ]+$/', $fields[ 'billing_last_name' ])){
        $errors->add( 'validation', 'Last name should only have no special characters.' );
    }
}