I'm trying to use a Jira automation rule to create a new Confluence page whenever a task is created in a specific project.
There's an answer here that indicates it can be done via a web request.
I've set up my rule and am testing it using the Validate Your Webhook Configuration at the bottom of the rule. I keep getting this error response:

I'm sending the Authorization header correctly, as far as I know; the blurred value is the base64 encoding of my account's email address:my API token.

If I just paste that URL into my browser, I get the expected json response of page data, so why is it not working via the webhook? I am a site-admin for both Jira and Confluence and have admin access to the space I'm trying to create the page in.