Does it mean the customer's in command? (5)

I believe the answer is:

order

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'command?' is the definition.
(I know that order is a type of command)

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for order that I've seen before include "Direct - sequence" , "Instruct" , "Directive or society" , "See 20" , "Direct or requisition" .)

I've seen this clue in the Evening Standard.

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