How to restrict user to chat with another user based on their payment and subscription? I'm new to Drupal. I need to make a consulting website, where I need to restrict user from chatting. The user can chat only with the consultant they paid for. User can participate in forums as they are free of cost. 

Any suggestions about how to implement this?

Note: for normal chat concept, I use DrupalChat.
From the DrupalChat project page:


  ... provides optional integration with ... Flag Friend module.


And issue # 936350 states:


  ... Would it be possible to show only friends from the Flag Friend module?


Since this issue has status closed(fixed), you should be able to use the Flag Friend module like so:


After the payment was completed, grant the user some permission to be allowed to "flag" the consultant the user paid for.
After such flagging is done, the user should be able to chat with such consultant.