Functionalab.com typically allows only one promotional code to be used per transaction. This means that if a customer has multiple promotional codes, only one of them can be applied to an order. However, certain promotions might not always be combinable with other discounts, sales, or offers. It is advisable for customers to carefully read the terms and conditions associated with each promotional code to understand its specific limitations. For the most accurate and up-to-date information regarding current promotional offers and their applicability, customers may check the official website. This should provide all the necessary details to help customers take full advantage of available promotions.