docs: verify the production Slack request URL after adding its secret

Author: jackbridger

docs/guides/example-projects/resend-email-agent.mdx

@@ -134,10 +134,11 @@ You need a Trigger.dev project, a Resend inbox on a verified domain, a Slack wor
 
 To deploy, run `npx trigger.dev@latest deploy`. Production has its own `resend` and `slack` endpoints, with their own URLs and secrets:
 
-1. Create a second Slack app from the manifest with the production `slack` URL, install it, and use its bot token as `SLACK_BOT_TOKEN` in production. A Slack app sends its clicks and replies to one URL, so dev and production each need their own app.
-2. Point a Resend webhook at the production `resend` URL. Disable or delete the dev webhook, or use a separate inbox for dev, so the same email doesn't get drafted twice.
-3. Paste each signing secret into the matching production endpoint. Until then, the endpoint shows "Needs secret" on the Webhooks page.
-4. Set the other environment variables on your production environment as in dev.
+1. **Slack:** create a second Slack app from the manifest with the production `slack` URL. Paste its Signing Secret into the production `slack` endpoint, then click **Verify** in the app's Event Subscriptions. Install the app and use its bot token as `SLACK_BOT_TOKEN` in production. A Slack app sends its clicks and replies to one URL, so dev and production each need their own app.
+2. **Resend:** point a Resend webhook at the production `resend` URL and paste its signing secret into the production `resend` endpoint. Disable or delete the dev webhook, or use a separate inbox for dev, so the same email doesn't get drafted twice.
+3. Set the other environment variables on your production environment as in dev.
+
+An endpoint without its secret shows "Needs secret" on the Webhooks page.
 
 ## Relevant code