landing_site is blank in webhook

[UCBoxes]

We have a webhook that is fired when an order is created. We are using "landing_site" to get the url parameters.

We want the url parameters to be captured when users visit our site and the same will be passed to webhook.

We are using the following link

https://www.ourdomain.com/index.php?referrer=affparam1&keyword=affparam2

It works sometimes, not always, not sure what is wrong. Can anyone help?