Issue sending issue_url via custom payload to Slack

[Jahnavi]

Hi, I am setting up an automation that sends custom data to Slack webhook. 

I can send key, description, and other fields using the smart values but when I try to send the URL of the issue using the below format, it keeps failing. 

"hyperlink":

[

  { "text": "{{issue.key}}",

      "url": "https://xxxxxxx.atlassian.net/browse/{{issue.key}}" 

   }

]

I am unsure if this is a Jira or Slack limitation or if my formatting is wrong. I would appreciate any input!