Hi @ramesh, 

I’m not super familiar with how this github article in particular is documented, but Klaviyo does have an article that covers how to use Track API for these custom properties. You can find that reference article here: https://www.klaviyo.com/docs 

Specifically, in the case of Track API’s, you’d want to put your additional properties in the “customer properties” line item. Make sure you are not putting the parameters under “properties”, as that is reflected as an Event instead of a Customer Property. This is an example: 

{
  "token" : "SkNuFx",
  "event" : "Louisiana Purchase",
  "customer_properties" : {
    "$email" : "thomas.jefferson@klaviyo.com"
  },
  "properties" : {
    "$event_id" : 10001234,
    "$value" : 11250000,
    "From" : "France",
    "SquareMiles" : 828000
  },
  "time" : 1609276614
}

I hope this was helpful!

Additionally, the Klaviyo Community is a hub for all Klaviyo customers, partners, and the extended Klaviyo ecosystem to network with one another and share their experiences throughout their e-commerce journey. Although this platform is not monitored by Klaviyo Support team members, many other users and partners are eager to help one another and provide guidance on Klaviyo! We hope to learn more about your experiences and hear about your successes as well. 

Cheers to you and wishing you a very happy new year, 
-Cass.