This article is intended for Citrix administrators and technical teams only.
 
Non-admin users must contact their company's Help Desk/IT support team and can refer to CTX297149 for more information.
 

The following error is returned by the Citrix Gateway to Citrix CWA app when application/desktop launch fails:
Failed to launch session <session_name>. Error code: 2502

This error indicated that backend VDA is unreachable for Enlightened Data Transport. 

To resolve this issue check firewall rules for UDP reachability to VDA,