If it's the first session and you cannot accomplish the client's goals, you can optionally issue them a refund.
In an ideal scenario you were upfront as early into the session as possible that the client may not be able to walk away with the problem solved. In many cases, knowing what won't work is actually helpful to clients, so they wish to proceed regardless. If they are still expecting their work finished, though, there's a high probability that they'll resent being charged.
If you'd like to process a refund please notify [email protected] and we'll take care of it for you.