Payment is for transportation (5)
I believe the answer is:
taxis
'payment is for transportation' is the definition.
I can't tell whether this defines the answer.
'is for transportation' is the wordplay.
'for' says to put letters next to each other (I've seen this in other clues).
'transportation' becomes 'tax' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'is' put after 'tax' is 'TAXIS'.
Can you help me to learn more?
(Other definitions for taxis that I've seen before include "Cars with a driver for hire" , "Cabs" , "return to right place" .)