Capital I invested in comfortable seating? (5)

I believe the answer is:

sofia

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'capital' is the definition.
(capital of Bulgaria)

I don't understand how the remainder of the clue works.

(Other definitions for sofia that I've seen before include "Capital of Bulgaria" , "capital city" , "Bulgarian capital" , "Bulgarian city" , "Foreign city" .)

I've seen this clue in The Times.

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