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'clear' here means that the payment is to be authenticated by the bank as real.
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In banking and finance, clearing denotes all activities from the time a commitment is made for a transaction until it is settled. This process turns the promise of payment (for example, in the form of a cheque or electronic payment request) into the actual movement of money from one account to another. Clearing houses were formed to facilitate such transactions among banks.

https://en.wikipedia.org/wiki/Clearing_(finance)
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