The API currently returns an empty response. To get a complete response, we need to run the following query to retrieve the siteId covered by the API:
SELECT srv.site_id
FROM SRD_ROUTER_VIEW srv
INNER JOIN ELEMENTADDITIONALINFO edi
ON srv.id = edi.ElementId
WHERE attribute = 'NE_Network_Position'
AND value = 'PE';

The siteIds parameter must be Site IDs of PE routers, visible in SRD UI under Inventory → Router (Site ID column). The test environment has no PE routers configured (NE_Network_Position = PE not set on any router in NEP inventory), which is why the API returns empty. Valid testing requires at least 2 PE routers configured in NEP inventory.

Previous list is got from the sql code shared by Ayed, which include "value = 'PE" :

SELECT srv.site_id
FROM SRD_ROUTER_VIEW srv
INNER JOIN ELEMENTADDITIONALINFO edi
ON srv.id = edi.ElementId
WHERE attribute = 'NE_Network_Position'
AND value = 'PE';

find attached sample request from 84 server :
forget the query you must copy two site ids from the report in SRD UI, link of report : http://10.164.144.84:9189/NEP_SRD_UI/reporting/router

The output is fine now, but there is a performance issue now : 6s on OLD, versu 11s on NEW. See screenshots

fixed available with release 53