Elavon Converge Hosted Payment Page Call back URL not being hit

Question

I am using Elavon converge's hosted payments page integration method. https://developer.elavon.com/products/converge/v1/hosted-payments

I am able to successfully get a session token and redirect to a payment page using it. Now, I want to setup a webhook that consumes the result of the transaction, so I can maintain/process the payment internally.

I am running a simple dummy python http.server on my local and using ngrok to get a public url for this server.

Now, the problem is it is unclear how to specify the call back webhook. https://developer.elavonpaymentgateway.com/#!/hpp/transaction-processing This page talks about it but seems outdated and not specific to the new hosted payment page integration method.

https://developer.elavon.com/products/converge/v1/supported-transaction-input-fields

This page mentions a param named ssl_callback_url but adding this param to my transaction_token call doesn't do anything. I want to hear back the response of my transaction to my local server.

I have tried adding ssl_callback_url parameter to my session token call. I have also tried adding the url to the converge portal under export settings but that doesn't work either.