Lists the plans the given NPI has negotiated rates for in the given rate sheet, as one row per distinct payer and plan pair. Takes no query parameters: an NPI and a sheet in, every plan in that sheet for that NPI out. The sheet may be a linked sheet, in which case only the rows that sheet shows are considered. A malformed NPI is a 400, but a well-formed NPI the sheet holds no rates for is a 200 with an empty plans list - that is a successful answer, not an error, and it does not distinguish an NPI that does not exist from one with no rates in this sheet.