Ping is a lightweight endpoint used to confirm that an API credential is valid.

A successful call confirms the request reached the server and the token was accepted.
The response reports whether the request is authenticated and which merchant it resolves to.

The Ping endpoint supports a single health check call.
A response with a merchantId confirms the API key is valid and requests can proceed.
A missing or null merchantId means the API key, client ID, or client secret should be checked.

* GET /pay-int-api/ping.
Confirms the request is authenticated and returns the merchant it resolves to.