No client is going to pay for a session with an independent escort via an on-line directory pay facility.
Likewise, no escort would use that as a means of receiving payment.
What's in it for either party?
Also, why would a client contact your customer services to access an escorts availability
in preference to phoning her direct?
Where is your revenue stream?
Is this off the escorts fee
or is it top loaded?
If the latter, why would a client bother in preference to dealing with the escort direct
where appointment arrangement is 100% accurate as there is no middle man,
and presumably cheaper...

I don't see a viable business model here,
and for that reason, I'm out.  



edit
1.CPS.gov.uk/Exploitation of prostitution
2. SW5 info on same
There may be an aspect of "Controlling a prostitute for gain" element too,
but I'll let wiser heads take up that observation...

Sometimes we can think something is a good idea but if you think about it, if it had been that good an idea then someone else would have done it decades ago.

Reason it hasnt been done is usually because it isnt viable.