How to get price from secondary price list using pricing API

Hi,

We have a Service price list and then additional secondary price lists for each customer (with qualifiers as bill to for the customer).  When we create an order with Service price list at the header level and add an item from the secondary price list on lines, the price comes up correctly.  I need to achieve the same from API call, but when I pass Service price list id as the starting price list, I get the message that item is not on the price list.  The API does not go on to look for secondary price list based on