As an IT professional, I find it annoying that these systems do not work better for the users. There is little or no reason both cannot exist, and work well. Email and IM systems are fairly mature, meaning they can be used on sites like this without the difficulties being experienced, even "out of the box". I know, because I've done it - initial and subsequent notifications going out in a timely manner.
The concept of a the chat app seems misguided. Nice if both are on, but if escorts need to keep their second job on the downlow, having an app on their phone is not a good way to do it.