If night audit button is grayed out, It means the particular user does not have the privilege/rights to perform night audit.
In order to assign privilege for night audit process, please refer below mentioned steps:
Path: Select Configuration(Login as Admin) >> User (button) >> Select the particular User >> Edit >> Operational privilege >> Check mark on night audit option >> Save.
Screenshot 1:
Restart eZee Frontdesk to apply the changes and check the same.