fix: update the additional details for 3200 errors (ngrok#576)

Signed-off-by: Russ Savage <russ@ngrok.com>

docs/errors/details/_err_ngrok_3200.md

@@ -1,11 +1,16 @@
 ### Additional Information
 
-This means your ngrok agent is not online.
+This error occurs when there is no active tunnel using the hostname you are trying to reach. There can be multiple reasons why a tunnel that you expect to be running is showing a 3200 error.
+
+If you are the ngrok Administrator for this account, please verify that the ngrok Agent is running and that the subdomain/hostname is correct.
 
 ### The most common causes of this error are:
 
-- You forgot to start your agent. First, try to restart your agent.
-- The endpoint that ngrok has provided has changed. This can happen if you have restarted your ngrok agent due to a change in configuration or a session timeout. To avoid session timeouts, register for a [free ngrok account](https://dashboard.ngrok.com/signup) and install your authtoken by following this [getting started guide](https://dashboard.ngrok.com/get-started/your-authtoken).
-- Your ngrok agent is having trouble reaching the ngrok service. Try running the [`ngrok diagnose`](https://ngrok.com/docs/agent/#troubleshooting-connectivity) command to check for connectivity issues.
+- The ngrok Agent is no longer running, or you forgot to start the Agent. Verify that the Agent is running and showing the expected "Forwarding" address.
+- The Agent session has timed out or stopped. Restart the ngrok Agent to restart the Agent and tunnel sessions.
+- The endpoint domain/hostname has changed. If you are on the Free plan or have not set the `--domain` flag to set the domain on the tunnel, please be aware that the forwarding address will change each time the Agent and session are restarted. If you previously obtained a forwarding URL from an agent session but have since closed that session or closed the client window, the URL will change when a new Agent session starts.
+- You have made a typo in the endpoint address you have entered in the browser. Verify that the tunnel hostname is correct. Incorrectly entering the address (a typo) in a browser address bar can also result in this error.
+- A network issue exists between the device the Agent is running on and ngrok. Your ngrok agent might have trouble reaching the ngrok service. Try running the [`ngrok diagnose`](/docs/agent/cli/#ngrok-diagnose) command to check for connectivity issues.
+- You are attempting to run `--scheme http` on your agent using a domain that only supports https. All of the `.app` and `.dev` domains are HSTS or "HTTP Strict Transport Security" domains. Paid plan accounts are able to start http scheme tunnels on the `ngrok.io` domain, which is not HSTS enforced.
 
-If you have additional questions or none of these steps work for you, drop us a note at [support@ngrok.com](mailto:support@ngrok.com?subject=Help%20with%20ngrok%203200%20error).
+If you are the Administrator for this account, and none of these steps work for you or you have additional questions, drop us a note at at [support@ngrok.com](mailto:support@ngrok.com?subject=Help%20with%20ngrok%203200%20error).