JSON-RPC API is deprecated.
Most of the API functions will take "publisherToken" as their first parameter (48-character key).
The Publisher Token is used to identify the merchant (the seller). This token is used to create and update offers, as well as gives access to other e-commerce functions (like reporting).
It can be obtained from API Keys Page (you must be logged in to Cleeng as a publisher to see this page).
Important: never expose your Publisher Token to the public. It will allow price updates and other sensitive data access.