I need to add the store location to my documents but I don't know where to pass it in a GetTax Request.
The LocationCode (string , required only if outlet-based reporting is needed, otherwise optional) also referred to as a Store Location, Outlet Id, or Outlet code is a value assigned by some State jurisdictions that identifies a particular store location. These States may require tax liabilities to be broken out separately for each store Location. Otherwise LocationCode is just a reference property that you can use to search for specific store locations in reports.
Note: This property is not currently available in the Avalara REST service.