There is a recognisable kind of message that arrives late in the night. It is short, it is polite, and it is missing most of what would let anyone answer it. Something like: hi, are you available. Sent at ten to four, from someone who has been awake for twenty hours and has used up the part of their attention that handles detail.
Nothing about that message is wrong, and it always gets somewhere eventually. It just takes three exchanges to reach a point that one message could have reached, and at ten to four three exchanges is a long time.
The four things that go missing
Consistently, and in this order.
The hour. Not now, which is less precise than it sounds, but an actual time. There is a difference between as soon as possible and half past four, and the difference matters when the arrival window is forty to sixty minutes from confirmation. If you mean the soonest possible start, write that phrase rather than leaving it implied.
The length. The rungs are an hour at EUR 180, ninety minutes at EUR 270, two hours at EUR 360, three at EUR 540, and the eight hour night at EUR 1,250. A message without a length cannot be answered with a price, so it forces a question that costs both sides a round trip.
The address, roughly. Not the room number, which comes after confirmation, but the area, the floor, and anything the entrance needs after hours. A booking at four in the morning to a building with a coded street door and an unmentioned code is the one genuine failure mode of a night arrangement.
How many people. One guest or two. The figures differ completely: EUR 180 an hour for one guest with one therapist, EUR 360 an hour for a couple with one therapist, EUR 360 an hour for one guest with two, EUR 720 for a couple with two. A message that does not say cannot be quoted.
A message that works, at any hour
Everything above fits in four lines and takes under a minute even at the end of a long night. The hour you want, the length from the ladder, the format, the area with the floor and the entrance, and whether it is one of you or two. Add a line about a preference if you have one, and a line about anything that has to be worked around. The booking page keeps the same list in the same order.
What makes this worth doing at ten to four specifically is that you are writing at the worst moment of your own day for composing anything. The message you send now is the one you will be asked to clarify in ten minutes, and clarifying is harder than writing was.
What not to put in it
Nothing sensitive, and nothing that belongs later. The exact room number goes in after the booking is confirmed, in the same thread. There is no reason to send a photograph of anything, no reason to send a document, and no reason for money to move anywhere except to the destination named in the thread after the hour is agreed. Anything that arrives claiming to be the house from some other direction is not the house. This site has one written address and no phone number or handle anywhere in its pages.
Why the written thread suits this hour
Because it can be scrolled back. A figure typed out at four in the morning is still legible at four in the afternoon. A start time in writing settles any later question about notice, which matters because the whole notice scale is measured from when a message lands. A door code in a thread cannot be half heard. And a guest who is tired can take four minutes over a paragraph without anyone waiting on the other end of a line.
The one thing to check before sending
Read it back and ask whether someone who knows nothing about your night could act on it. If the answer is yes, send it. If the answer is that they would have to ask you two things first, add those two things now, while you still have the attention to write them. At ten to four that is the entire difference between a booking that starts at half past and one that starts at five.