Payment is always a very individual matter, and it is undoubtedly wise to be smart about it.
I would not want the money transaction to anyhow disturb the spontaneous development of our meeting in any way.

Payment, always in cash, is most of the time made a few minutes after the beginning of the meeting, but this is not an essential rule.
If my client and I agree to begin our meeting outdoors, I would surely not expect the client to carry the money with him same as assuming myself to be paid right away. I would most likely feel anxious for both the client and me for getting robbed during sightseeing. Do not misunderstand me please, Prague city is overall very safe, but the Prague downtown is unfortunately well known for the petty crafty thefts.

I would, therefore, recommend to anybody to lock all the money in the hotel room safe and carry just a very little cash and a credit card instead. I have no issues myself waiting for the payment until we get back to the hotel room.

Do always have the stated sum of money ready, preferably in a discreet unsealed envelope or a gift card.
Once being indoors and discreet, my clients usually places the unsealed envelope or gift card with my name on it on the table or some another visible place without commenting on it, and that’s it. Once I will take the money, I will surely notice you about it.

Also, I never do ask nor request any money to be transferred to me as a deposit before the meeting.