Tableau Server Error "The product key <key> has already been activated"

To understand and resolve the issue with the Tableau Server activation stating that the product key has already been activated, review the following:

If the key is activated and showing in TSM:

Run TSM Licenses list command or review the keys in the TSM UI. For more information, see View Server Licenses.  If the product key does display, it will not be possible to activate the key again.  No further action is necessary as long as Tableau Server has been restarted since the key(s) were activated. 

If the key does not match the Tableau Customer Portal but has an updated expiration date:

After running the TSM Licenses list command or viewing keys in the TSM UI, the product key is not updated to match the key listed in the Tableau Customer Portal, but the subscription term expiration date does match the Tableau Customer Portal. No further action is needed.  Once the previous expiration term has occurred, the key will change to match the key in the Tableau Customer Portal.  

Non-ATR Activations and the key is not listed in TSM

If the Tableau Server is not able to read the product key stored in memory and the key is not listed in TSM (not ATR activations), perform the following:

1. Open a command prompt from the initial node 
2. Navigate to the Tableau Server bin directory, located by default at:
   Linux: /opt/tableau/tableau_server/packages/bin.<version_code>/
Windows: \Program Files\Tableau\Tableau Server\packages\bin.version_code 

• Run the following commands one at a time:  
  Note: these steps will stop the Tableau Server and cause down time.
  tsm stop
./lmreread  (linux) or lmreread (Windows)
tsm start
tsm status -v

Offline Activations (Non-ATR)

If an offline deactivation file has been created on a specific license key but the process outlined here has not been completed, this error will occur when trying to activate the key again.  Complete the offline deactivation, which will include a TSM command to process the deactivation file (tsm licenses deactivate -f <path-to-license-key-return-file>).  Once this is complete, then the key can be activated again.