Wordpress 3.1 ?
What do you mean ? This plugin was recently introduced some months before when wordpress version was 3.4.
This plugin needs API key to work from the very begining. The API key is to make font conversion request. The API key can be obtain by paying or using free key as well.
Only difference is that Free key only allows single font conversion where as paid key supports unlimited.
We have a dedicated team for the plugin development and support. This guys will be helping and supporting you in very step.