You have a ProxySG running an SGOS version prior to 184.108.40.206 and you are trying to download CASB Audit App Attribute feed functionality.
You are unable to download CASB Audit App Attribute database and you are seeing this error:
% Invalid response "426" from Apps Attributes Service
Upgrade to SGOS 220.127.116.11 or later to address this issue and for the full support of the CASB Audit Attribute feed functionality.
NOTE - SGOS 6.7.4 EA versions will not address this issue. Such as 18.104.22.168 , 22.214.171.124 , 126.96.36.199