Implementation of Purchase plugin

We are trying to integrate the purchase plugin in our application,where we have some products to buy,we are able to figure out the csp url fetches the information about the assets which gives us the asset id,but when we try to buy/subscribe using the purchase plugin we are not sure,whether we have to navigate to the our payment gateway or metrological billing store.Can team help us with that,is there any previous implementation done on purchase plugin.Here are the links we referred.

cspbackend: GitHub - Metrological/payment-csp-backend-example

There is an issue in SDK that seems similar to this question, i suggest taking a look at: Purchase Plug-in How we can use? · Issue #289 · rdkcentral/Lightning-SDK · GitHub and do some follow-up there if needed