The balance, handed over when she arrives
The balance is the second half of the fee, handed over at the start of the visit rather than at the end, and it is settled in the room itself.
Whatever did not go ahead is settled once the door is shut and her coat is off. Not at the end of the visit, and not partway through it.
Cash, and other currencies
Cash is the straightforward way to settle a balance in the room, and euro is the currency every figure on this site is written in. If you are carrying another major currency and would rather pay in it, that is welcome, with one condition attached: the exact amount in that currency is confirmed to you in writing before she leaves, so that nobody is doing arithmetic on a doorstep. Nothing is worked out on the spot and nothing is estimated.
Why the start rather than the end
Because an hour that opens with money settled is an hour that can be spent on the thing it was booked for. Leaving it to the end puts a small transaction at exactly the point where nobody wants one, and it turns a clean finish into an administrative one. It also means that if something about the room has changed since the thread was written, it gets said in the first two minutes rather than the last two.
Nothing is added later
The figure agreed in the thread is the figure. No travel charge inside the city, no charge for an hour late in the evening, no seasonal surcharge in December and none in a heatwave. Where a session finishes early, the fee for the reserved time stays as it was and nothing whatever is added on top. The roster prints every figure in full.