International clients in trouble must accept answer lacking flexibility (9)
I believe the answer is:
inelastic
'lacking flexibility' is the definition.
(elastic can mean flexible)
'international clients in trouble must accept answer' is the wordplay.
'international' becomes 'i' (abbreviation eg in IMF).
'in trouble' indicates anagramming the letters.
'must accept' means one lot of letters goes inside another.
'answer' becomes 'a' (abbreviation eg in Q and A).
'i'+'clients'='iclients'
'iclients' anagrammed gives 'inelstic'.
'inelstic' placed around 'a' is 'INELASTIC'.
(Other definitions for inelastic that I've seen before include "without resilience" , "Not stretchy" , "Supply not sensitive to price changes" , "stiff" , "Non-stretch" .)