After authorizing ArcGIS Server on a new machine, attempts to join the machine to an existing ArcGIS Server site fail, and return the following error message:
Error: Failed to join the site '<SiteURL>'. The license of ArcGIS Server at '<MachineName>' does not match with the license of the site running at '<SiteURL>'. All the machines in the site are required to have the same license.
The license in the generated keycodes file of the newly authorized ArcGIS Server machine does not match the keycodes file used in the existing site.
Ensure all the ArcGIS Server machines are authorized with the same license and have matching keycodes files. This allows the new machine to join the existing site. Refer to ArcGIS Server: Considerations before joining a site for more information.