Immune to influence, Victor props up dodgy prime debt instruments (10)

I believe the answer is:

impervious

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'immune to influence' is the definition.
I can't tell whether this defines the answer.

'victor props up dodgy prime debt instruments' is the wordplay.
'victor' becomes 'V' (phonetic alphabet: alpha, bravo, charlie etc.).
'props up' means one lot of letters go next to another.
'dodgy' indicates an anagram (a dodgy or wrong order of the letters).
'debt instruments' becomes 'IOUs' (IOU is an example).
'prime' with letters rearranged gives 'imper'.
'v' put after 'imper' is 'imperv'.
'imperv'+'ious'='IMPERVIOUS'

Can you help me to learn more?

(Another definition for impervious that I've seen is " impossible to pass".)

I've seen this clue in The Times.

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