When starting the Railgun service for the first time, you may see an error that states: 

Starting railgun Error starting Railgun as a daemon. Running in foreground... Error activating: Activation Failed: Invalid or missing railgun token or tag.  [fail]

There are two possible causes for this error:

1. The railgun.conf file doesn’t have the proper public IP (activation.public_ip oractivation.railgun_host in newer versions of Railgun) and/or activation token (activation.token) configured.
   
   
2. There’s a chance the Railgun created for the domain in your account was not created properly. Delete it, create a new one, and try again.

If the issue persists after trying both of these steps, please contact support.