Unable to Change PHP Version

Version: Plesk 17.5.3
OS: Red Hat 4.4.7-17

I'm trying to add a new account and use php 7.1 fastCGI but I'm unable to do so. I've attempted to set the PHP version in:

Home>Domain>mydomain>PHP settings,
Home>Domain>mydomain>hosting settings
Domains > Manage in Customer Panel > PHP Settings
On the command line: /usr/local/psa/bin/subscription -u mydomain.com -php_handler_id plesk-php71-fastcgi

The Plesk panel shows that the PHP 7 has been selected but a...

Unable to Change PHP Version