VDA registration in Citrix Virtual Apps and Desktops fails with the error: "functional level too low for catalog."
Downgrade Machine Catalog VDA version to a equal or earlier version than the Installed VDA version. Higher version of the VDA software on the Servers/VDIs must be installed before upgrading the Machine Catalog VDA version.
You should select right functional level while creating machine catalog.
Machine Catalog VDA Version set to a higher version than the Installed VDA version.