Patrik,
Thanks for your efforts but the additional css seems to have created other FA-related issues elsewhere and I’m certain my servers allow PHP sessions as I have many instances of WP “cart” functions running trouble-free on those servers. I will however try adding
define('WPINV_USE_PHP_SESSIONS', false);
to the WP config file. I think my best solution is to find an alternative to Font Awesome, although being so widely used, that will be a challenge and I have other plugins which also use FA extensively. I think also I will need to find an alternative to “Invoicing” which is a great shame as it has a lot of promise and integrates well (in theory) to Geo Directory. I have a deadline of the middle of January to get this site working for a client and cannot afford the time to spend continually fault-finding. Again, thank you for your efforts.