Crossword Genius

Those serving drinks here canned? (6,4)

Ross

I believe the answer is:

behind bars

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'canned?' is the definition.
(both can mean in prison)

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

Can you help me to learn more?

(Other definitions for behind bars that I've seen before include "Serving time" , "Where to find convicts" , "Where alcohol is kept" , "Like staff serving drinks" , "Locked away" .)

I've seen this clue in The Telegraph.
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