For something that really appeals, you'll pay it happily (9)
I believe the answer is:
attention
'for something that really appeals you'll pay it happily' is the definition.
The definition suggests a singular noun which matches the answer.
This is all the clue.
Can you help me to learn more?
(Other definitions for attention that I've seen before include "Awareness - regard" , "Vigilance; care" , "should be paid to a teller's account?" , "Military command to adopt formal erect position (9)" , "Pay it and concentrate" .)