For example, demand for payment on return? Gentle reminder (5)
I believe the answer is:
nudge
'gentle reminder' is the definition.
(I've seen this before)
'for example demand for payment on return?' is the wordplay.
'for example' becomes 'e.g.' (short for 'exempli gratia', 'for example' in Latin).
'demand for payment' becomes 'dun' (a dun is a demand for payment from a creditor).
'on return?' is a reversal indicator (I've seen 'on return' mean this).
'eg'+'dun'='egdun'
'egdun' back-to-front is 'NUDGE'.
(Other definitions for nudge that I've seen before include "Give a reminder" , "Push gently" , "Gentle prod" , "Gentle encouragement" , "Remind (with the elbow?)" .)