The half that waits until she arrives
The balance is the part of the fee paid on arrival, in cash or by card, and it is settled at the start of the session rather than at the end of it.
Where half has already travelled, the balance is the other half, and it is handed over when she reaches you rather than when she leaves. Settling it at the start clears the only administrative thing in the evening out of the way in under a minute, which is the entire reason it sits where it does.
What it can be paid in
Cash in euro is the ordinary route, and card works too. Cash in another major currency is welcome, with the exact sum in that currency put in writing in the thread before she sets out, so nobody is converting figures in a hotel room on a Saturday night. Nothing is rounded up on the doorstep and no figure appears that the thread had not already named.
When it is the whole fee
A returning client asking for an hour or two at a city address later the same day sends nothing beforehand, so the balance and the fee are the same thing. On a first trip that case does not arise, since a first booking always carries a front half whatever the hour.
What it does not include
There is no travel charge inside the city, no weekend rate, and no surcharge for a late start. The figure agreed in the thread is the figure, and the halves of it are named there in euro before anybody moves. The full set of rungs for one guest and for two lives in each profile on the roster.