Pay attention: ready money's invested. Upset? Mostly upset (4,2,4)
I believe the answer is:
read my lips
'pay attention' is the definition.
'ready money's invested upset? mostly upset' is the wordplay.
I cannot quite see how this works, but
'money's' could be 'ps' and 'ps' is located in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for read my lips that I've seen before include "Electoral pledge (to deaf audience?)" , "I promise you" , "Listen carefully!" .)