Andrea, yes you can use the chat in the voice-only mode. You can turn your camera off and enable the microphone only. Also, Mozilla Firefox browser allows you to chose whether you want to 'allow' both camera and microphone or microphone only when you start the conversation. Finally, if you want to completely remove the video option, you can make small changes in the plugin code. You should open the following file videoim/static/js/videoim.js, find this string
getUserMedia({audio: true, video: true}, gotStream, function ()
and replace with this one
getUserMedia({audio: true, video: false}, gotStream, function ()

As for the User Credits - you can configure it in two ways:
- charging users per minute;- receiving/losing credits for each outgoing/incoming calls;
You can chek this on our demo. Simple login as the site admin go to Admin Area > Plugins > Installed Plugins > User Credits >> Settings.
Let us know if you have further questions.

thank you so much!

Yes, you are right, there is no SSL for now, but we are working on this issue and it will be fixed within a couple of days.

If the problem does not exist at our demo site, so seems the problem with your SSL certificate. The certificate should not be self-signed and to test the chat your should emulate real conversation. i.e. using two different computers and two different users. Also, you should allow your browser to use the camera and microphone.

Finally, please test your camera and microphone to be sure that they are working correctly:

Test camera: https://www.onlinemictest.com/webcam-test

Test microphone: https://www.onlinemictest.com/