Electric car (posh) only with Romania; it’s a mistake (5)
I believe the answer is:
error
'electric car posh only' is the definition.
I can't judge whether this defines the answer.
'with romania it's a mistake' is the wordplay.
'with' indicates putting letters inside.
'romania' becomes 'ro' (international vehicle registration code).
'it's a mistake' becomes 'err' (I've seen this in another clue).
'ro' going inside 'err' is 'ERROR'.
Can you help me to learn more?
(Other definitions for error that I've seen before include "Blunder or mistake" , "Mistake from terrorist" , "Boob" , "Bug" , "Trial and ___" .)