You are NOT required to communicate through their website to have your review posted. Their system of checks and balances, while not perfect, is designed to prevent a plethora of fake reviews. All you need to do is to be logged on to their site and obtain the service provider's phone number. Rentmasseur's system will track your site activity, which in turn will allow your review to be reviewed and posted.
P.S. It also helps to have the masseur on your wishlist, but it is not a requirement. Further, if you have have communicated with the masseur over text, you should send a screen shot of the text message to the body of your communication with the RM administrator (I have done it in the past and the review was posted).
I'm happy to answer any additional questions you have. Please do a reply to this message so it pops up in my alerts.