Impossible to answer if you do not give contextual information about your installation and setup. Do you use FreePBX, from your answers my guess is that you don't, but it is a guess.
If you tell what do you use in the backend, how did you install and configure FOP2, then I will be able to tell you about plugin installation.
As a rule of thumb, you must use the FOP2 Manager, you must leave the #exec autoconfig-users.sh line in fop2.cfg and avoid using any other user=xxx or buttonfile=xxx lines in it. You must be using a recent FOP2 version (2.28 or higher). If any of the above is not true, then you will find issues or plugins just won't work.