Get Orders from External Ressource

So, I tried today to insert orders to Shopware via API using file client.php, how is explained in the book “SW Das handbuch fur Entwicller” page 293. It works but I inserted hard coded data:

require 'client.php';

$client = new ApiClient(
  'http://shopware567.loc/api',
  'admin',
  'nUeRFUr998dE8lD2xXF0QzPbJbOLFuAroingElhJ'
);

$result = $client->call(
  'orders',
  'POST',
  [
    'changed' => '2020-07-28T10:25:45+0200',
    'number' => '20003',
    'customerId' => '1',
    'paymentId' => '5',
    'dispatchId' => '9',
    'partnerId' => '',
    'shopId' => '1',
    'invoiceAmount' => '350',
    'invoiceAmountNet' => '340',
    'invoiceShipping' => '6',
    'invoiceShippingNet' => '8',
    'invoiceShippingTaxRate' => '5',
    'orderTime' => '2020-07-23T10:00:05+0200',
    'transactionId' => '',
    'comment' => '',
    'customerComment' => '',
    'internalComment' => '',
    'net' => '0',
    'taxFree' => '0',
    'temporaryId' => '',
    'referer' => '',
    'clearedDate' => '2020-07-23T10:00:05+0200',
    'trackingCode' => '',
    'languageIso' => '1',
    'currency' => 'EUR',
    'currencyFactor' => '1',
    'remoteAddress' => '',
    'deviceType' => '',
    'isProportionalCalculation' => '',
    'attribute' => [
      'id' => '2',
      'orderId' => '2',
      'attribute1' => '',
      'attribute2' => '',
      'attribute3' => '',
      'attribute4' => '',
      'attribute5' => '',
      'attribute6' => ''
    ],
    'customer' => [
      'id' => '1',
      'email' => 'my-email@mail.com'
    ],
    'paymentStatusId' => '13',
    'orderStatusId' => '1',
    'billing' => [
      'countryId' => '2'
    ],
    'shipping' => [
      'countryId' => '2'
    ],
  ],

);

I copied the GET response and created the POST request with the same data structure but could not post because some parameters like billing, shippint where missing. I added them and succeeded to post. 
Now, how to fill the data structure for POST request with real data from OTTO response? Some necessary dada is possilbe to extract but some are not present or have different format. For example in OTTO the order number is like this “bk22dvtvdm”, in Shopware looks like this “20003”?