Secured by advance payment, I start to make a living (7)
I believe the answer is:
animate
'living' is the definition.
(synonyms)
'secured by advance payment i start to make a' is the wordplay.
'secured by' is an insertion indicator (inserted letters are held or secured).
'advance payment' becomes 'ante' (I've seen this before).
'start to' suggests taking the first letters.
The initial letter of 'make' is 'm'.
'i'+'m'+'a'='ima'
'ante' enclosing 'ima' is 'ANIMATE'.
(Other definitions for animate that I've seen before include "Give inspiration to" , "Enliven, alive" , "Instil life into - say cartoon" , "Spirited" , "Make lively like cartoon" .)