On the VDA server event viewer - "Event: 1050 Connection validation failed on domain for user for reason Unlicensed" 

1. Renew or reissue a valid certificate to license server
2. Install the certificate on server and export the .pfx file
3. Install openssl tool
4. Navigate to the \bin folder.
5. Run openssl pkcs12 -in C:\ls_cert\server.pfx -out server.crt -nokeys
(Note: The License Server uses only the .crt certificate format)
6. Type the password created during the export process (password).
7. Run openssl pkcs12 -in C:\ls_cert\server.pfx -out server.key -nocerts –nodes
8. Type the password created during the export process (password).
9. Copy the server.crt and server.key created above to cd \program files (x86)\citrix\licensing\WebServicesForLicensing\Apache\conf\
10. Restart the Citrix Licensing services on Licensing server and Citrix Broker Service on controller server 
11. Reconnect to licensing server from Studio console > Licensing configuration 

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Problem Cause

Certificate being used for licensing server expired , server was untrusted on controller .