woocommerce_add_payment_method_form_is_valid filter-hook . WC 1.0

Usage

add_filter( 'woocommerce_add_payment_method_form_is_valid', 'filter_function_name_1100' );
function filter_function_name_1100( $true ){
	// filter...

	return $true;
}

$true

-

Where the hook is called

if ( ! apply_filters( 'woocommerce_add_payment_method_form_is_valid', true ) ) {

Where in WP core the hook is used WooCommerce