Product IDs are more reliable than names, as they are unique to a product and never change. Whereas a name might change, an ID will remain the same. The other reason we use product IDs is that names are variable in length. IDs on the other hand are of a consistently short length which allows us to squeeze more into Campaign Monitor’s 250 character limit on custom fields.
Don’t worry though, product IDs are easy to find! Just find your product in the Shopify admin. The address bar should end in ‘.../products/123456789’, and the number here is your product ID.