What is a "duplicate" Lookup API call?

Duplicate Lookup calls have the exact same data as a previous Lookup (essentially, a cached call). Each Lookup is 'fingerprinted', so a duplicate call is an exact replica of an API call that's already been sent to TaxCloud - for which we've already provided an 'answer' (i.e. the tax amount due). The problem with duplicate calls is that they slow down the system unnecessarily.

Duplicate/ redundant calls can happen for various reasons. For example, please make sure your shopping cart is not re-sending a Lookup request each time a customer moves from one page to another after placing an item in his/her shopping cart. Also, make sure your cart is not re-sending Lookup requests each time a customer moves from one field to another when entering his/her address information at checkout.

It shouldn't be hard for your developers to figure out why the shopping cart is re-sending the same Lookup API calls.