Plesk API 404

Suddenly without warning our whmcs started returning a – (hyphen) when trying to create a package, looked in /usr/local/psa/admin/logs/httpsd_access_log and saw 404 errors for enterprise/control/agent.php

The default plesk filename for the agent file begins upper case –

/usr/local/psa/admin/htdocs/enterprise/control/Agent.php

Whereas whmcs calls lowercase agent.php

Weird, anyway create a symbolic link from agent.php -> Agent.php:

cd /usr/local/psa/admin/htdocs/enterprise/control/

ln -s Agent.php agent.php