The internal reference number is an optional code that you can enter during checkout to link the fluid-hub order to your internal management system (ERP, accounting software, purchase register). It is particularly useful for tracking orders linked to specific projects, jobs or cost centres.
For all the details on how to use it and where to find it after the order, read What is the internal reference number? To use it as a search criterion among your orders, read How does the order search work?