WordPress at a glance
filter is not described

woocommerce_checkout_required_field_notice filter-hook . WC 1.0

translators: %s: field name

Usage

add_filter( 'woocommerce_checkout_required_field_notice', 'filter_function_name_4340', 10, 2 );
function filter_function_name_4340( $sprintf, $field_label ){
	// filter...

	return $sprintf;
}
$sprintf
-
$field_label
-

Where the hook is called

WC_Checkout::validate_posted_data()
woocommerce_checkout_required_field_notice
woocommerce/includes/class-wc-checkout.php 825
$errors->add( $key . '_required', apply_filters( 'woocommerce_checkout_required_field_notice', sprintf( __( '%s is a required field.', 'woocommerce' ), '<strong>' . esc_html( $field_label ) . '</strong>' ), $field_label ), array( 'id' => $key ) );

Where in WP core the hook is used WooCommerce

Usage not found.