Charge to cross Thailand's frontier's fair (4)
I believe the answer is:
fete
'frontier's fair' is the definition.
'fete' can be an answer for 'fair' (I've seen this before). I am not sure about the 'frontier's' bit.
'charge to cross thailand's' is the wordplay.
'charge' becomes 'fee' (fee is a kind of charge).
'to cross' is an insertion indicator (some letters cross or go round others).
'thailand' becomes 'T' (abbreviation on car registration plates).
'fee' placed around 't' is 'FETE'.
Can you help me to learn more?
(Other definitions for fete that I've seen before include "Elaborate outdoor party" , "Festival event" , "Outdoor festival" , "Lavishly entertain; charity function" , "Big outdoor party" .)