How to Respond to Slack Messages: Troubleshooting Callback URL Issues

Hi all, I need some help to understand how to respond to slack messages. I have a flor where the input start with the / command and I want the ability to return a confirmation and/or ask the required questions. I keep getting errors around the callbackURL (response_url), in short they prompt can not find this url which is in the original trigger message. I tried a number of different spellings/prompts such as Webhook URL= followUpUrl / response_url etc { "webhookUrl": "{{callbackUrl}}", "contentType": "JSON", "body": {"text":"Your message"} } Thank you!