How to track promoters for sales
We have promoters sending customers to our website and we need a way to track which promoter gets which sales. Lets say a customer was referred by promoter #1 to our website and this customer purchases a product. How do we create the option for the customer to input a promoter code for promoter #1 in an input field at checkout so that we may keep track of which promoters are making which sales?
Thank you in advance for your help!