Shackleton actually answered your question succinctly. Its what you say, more than what you do that will get you a ride with LE.
If, when you arrive at a providers incall you start asking what you are going to get for this amount or how much she will charge for that service, you will almost surly be asked to leave. That is what LE would do. If you have checked her reviews you should know what services she is offering and what is the proper donation for those services. Don’t discuss actions for money. She is a big girl and knows why you are there. You should also know why she is there, no need to discuss.
If I see a new provider and she starts trying to get me to say what I want to do for the money in the envelope I will pick up the envelope and say “sorry, my bad” and run like hell.
The idea of leaving the envelope on the table while taking a shower is a good one if it is the first time you have seen a provider. This will give her a chance to check out how much you have offered and if the amount is correct. If you come out and she says that the donation is wrong that is the time to fix it. Still try to do this without discussing money for a sex act. Escorting is not of itself illegal so she might say that the amount you enclosed is only enough for 10 minutes and then the ball is in your court. If she is ready to party then all is well and the clock is ticking. Still no discussion of pay for play.
We don’t talk about money and services. Offering anything of value for sex is prostitution and against the law and surly none of us here would ever break the law.