adding extra dollars for cleaning payable on arrival

I like my guests to add extra dollars for cleaning per stay.

This has to be paid upon arrival, since I have no prepaid system in place. (don't like the hassle with refunds etc. as I had 6 times a cancellation this season.) For B only.      Nothing cancelled for A platform. 

According to admin of B the invoice should show it to guests before paying. 

How does that invoice look? I have not seen one....

This year I haven't charged guests the extra with B. I completely forgot.   For A it is added automatically. 

So handy!  

Though I had half the amount of bookings through A  compared with B.

How do I tell my guest clearly the extra has to be paid upon arrival without upsetting them last minute?

Could B not create something similar as A has in place please. 

Or how do other hosts do this? 

Greetings 

Aaltje B.