Think there's just one payment left (4)
I believe the answer is:
feel
'think' is the definition.
(feeling is a kind of thinking)
'payment left' is the wordplay.
'payment' becomes 'fee' (I've seen this before).
'left' becomes 'L' (common abbreviation).
'fee'+'l'='FEEL'
'there's just one' acts as a link.
This may not be right. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for feel that I've seen before include "Experience, perceive" , "Fondle" , "Experience (an emotion)" , "16A [JUDGE]" , "Perceive by touch" .)