Front End PM Deduct Credits

Hi I am trying to help someone that has developed their site using WordPress and to be honest we are both novices. I am used to editing HTML and ASP pages and am not familiar with the WordPress plugins. My daughter has created a site and used the Front End PM plug in to send messages between users and admins however she want for the users to be able to purchase credits before they can send a message and when they have sent a message then a number of their credits are deducted. She have included the MoolaMojo plugin for the purchasing of credits however I have no idea how to get the Front End PM plugin to talk to the MoolaMojo plugin to deduct the credits when the user sends the message. Is there an easy way to do this? Is there a better plugin that MoolaMojo to do this? Or can Front End PM do this already?