Thanks for the response @bcworkz.
I carried out your suggestion which initially returned the following path:
/home/ftpuser/public_html/wp-content/temp
However, we still had the following line in the wp-config.php:
define(‘WP_TEMP_DIR’, dirname(__FILE__) . ‘/wp-content/temp/’);
After removing the above line from the wp-config.php, we refreshed the page we were echoing the temp folder directory too, but it was just coming back empty.
On that basis I assume the issue would be that the line to define the temp folder is missing from our php.ini?