Add downloadable attachment option (as mentioned in the changelog per 2023-07-27) for the entities:

• estimates
• external sales invoice
• sales invoice
• document: general document
• document: general journal document
• document: purchase invoice
• document: receipt
• document: typeless document

For example, get info and content from an attachment added to a SalesInvoice:

// Create the Moneybird client
$connection = connect($redirectUrl, $clientId, $clientSecret);
$connection->setAdministrationId($administrationId);
$moneybird = new \Picqer\Financials\Moneybird\Moneybird($connection);

// Get the sales invoices from our administration
$salesInvoice = $moneybird->salesInvoice()->find(394429746230855571);

foreach ($salesInvoice->attachments as $salesInvoiceAttachment) {
    var_dump($salesInvoiceAttachment); // dumps the API response object
    var_dump($salesInvoiceAttachment->download()); // returns the string of the file
}

In the background, when you call the download endpoint, you'll be redirected to a temporary URL that contains the file content.

From the API docs:

Download the attachment. The response will be a redirect to a temporarily available URL where the attachment can be downloaded. Use the Location header in the response to download the attachment.