Issuing invoices for a large number of recipients may take a considerable time to complete. A way of making the server respond faster is to instruct it to process the request asynchronously. This is achieved by using the header

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Prefer: respond-async

Then the server responds with

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HTTP/1.1 202 Accepted
Location: https://www.sendregning.no/identical/{number}/status

The location link can be used to monitor the progress of the request processing. As long as the server has not completed the processing, the response contains the number of invoices processed so far:

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HTTP/1.1 200 OK

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{
    "status": "ACCEPTED",
    "invoiceCount": 123
}

When the server has completed the processing, the response will be

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HTTP/1.1 303 See Other
Location: https://www.sendregning.no/identical/{number}