Jira automation: Send the list of changed field ids in web request

Question

I have a Jira automation in which I am trying to send the list of changed field ids in a web request. The automation is triggered correctly but the i get a blank "changedFieldIds"

Automation setup:

1. Trigger: for field change on multiple custom fields:

    customfield_26962
    customfield_10761
    customfield_11966
    customfield_27165
    customfield_27164

2. Send web request http url: https://demo7197940.mockable.io/imsjirawebhookhandler Method: http post Custom data:

{
     "ticketNumber": "issue.key",
     "sourceSystem":"Dealer Portal",
      "changedFieldIds":"{{#changelog}}{{fieldId}},{{/}}"
}

From what I have been able to research, both methods below should work, but I get blank in changedFieldIds