Not oddly looking up, you pay the photographer’s agent (4)
I believe the answer is:
hypo
This clue could be a double definition.
'not oddly looking up you pay' is the first definition.
Although both the answer and definition are singular nouns, I cannot see how one could define the other.
'photographer's agent' is the second definition.
The answer and definition can be both substances as well as being singular nouns.
Maybe there's a link between them I don't understand?
'the' acts as a link.
Can you help me to learn more?
(Other definitions for hypo that I've seen before include "Sharp needle" , "Fixer" , "Prefix denoting 'under' or 'inadequate'" .)