Doesn't work? Enable logging!
The php-fpm.log file is a great place to fault-find errors and get to the bottom of a problem. But be sure to enable logging for your specific worker pool. Or you won't see anything!
Example:
To enable error logging for the default [www] worker pool, add this line in the [www] section of your php-fpm.conf:
[www]
catch_workers_output = yes