I fly in, convinced of getting an endorsement (9)

I believe the answer is:

signature

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'endorsement' is the definition.
(signing something can mean to endorse it)

'i fly in convinced' is the wordplay.
'fly' becomes 'gnat' (type of insect).
'in' means one lot of letters goes inside another.
'convinced' becomes 'sure' (similar in meaning).
'i'+'gnat'='ignat'
'ignat' put within 'sure' is 'SIGNATURE'.

'of getting an' acts as a link.
This may not be correct. Some or all of it may belong to another bit of the clue.

Can you help me to learn more?

(Other definitions for signature that I've seen before include "Handwritten name" , "Distinctive characteristic" , "Identifying piece of writing, tune etc" , "One's mark" , "distinctive style" .)

I've seen this clue in the Evening Standard.

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