Webhook for slack returns error 400 no_text

There are some great articles on here that helped me set up a webhook to push updates to Slack via triggers. However, I am now trying to use "Zendesk Events" to notify a Slack channel that we've had new community posts/comment published

When I do this Slack returns error 400 no_text. I know the webhook is okay because if I change the request body to something simple a test works. 

I am wondering if I need to do some form of authentication or add a header in the request. Any help would be much appreciated. 

I've seen some posts in other communities that have this issue but haven't seen a solution that would work in Zendesk. 

Full disclosure, I am not a developer so I am relying on the Zendesk and Slack UI's to be able to make this work.