Notice types
WooCommerce uses 3 notice types: success, error and notice.
Success
A ‘success’ message when something is successful, for example after adding an item to the cart, or getting a shipping quote.
Error
An ‘error’ message triggered when something goes wrong, either user fault or code.
Notice
A generic notice type which is neither an error nor a success message.
Adding a notice
The main function is to add a notice is wc_add_notice. Once added, the notice is queued and will be output and cleared when WooCommerce outputs notices before a loop.
wc_add_notice( $message, $notice_type = 'success' );
Translating a notice
wc_add_notice(__('The notice I want to translate', 'my-text-domain'), 'error');
Using sprintf with WooCommerce notices
Always use sprintf when using WooCommerce notices. It makes code much easier to read.
wc_add_notice( sprintf('You must have an order with a minimum of %s to place your order, your current order total is %s.', woocommerce_price($minimum), woocommerce_price(WC()->cart->total)), 'error' );