Put the bus on as an extra (5)

I believe the answer is:

bonus

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'an extra' is the definition.
(I've seen this before)

'put the bus on' is the wordplay.
'bus on' anagrams to 'BONUS'.
Though, I'm unsure how the anagram is indicated.

'as' acts as a link.

Can you help me to learn more?

(Other definitions for bonus that I've seen before include "Additional award" , "Extra pay, perhaps at Christmas?" , "Additional wage" , "Extra payment, may be performance-related" , "Extra payment for good performance" .)

I've seen this clue in the Evening Standard.

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