wordpress短代码选择完整的XML而不是单行

I am trying to create a wordpress shortcode which returns the price of a book from an API.

Ideally, I would like to be able to create a shortcode with this format [currency_isbn13] but for the moment I'd be happy to just create a fixed shortcode for each book and currency.

After various attempts, I was able to put together the following php code, but it is not working as it should

function Price() {

$isbn13 = 9783899735215;
$url = 'https://api.bookdepository.com/search/lookup?isbn13='.$isbn13.'&clientId={redact}&authenticationKey={redact}&IP={redact}&currencies=GBP';
$sxml = simplexml_load_file($url);
print_r($sxml);
return $sxml->price;

}

add_shortcode('isbn13', 'Price');

I would expect the shortcode to return the price of the book, but I get the following:

How can I fix this? I'm sure it is very simple but can't figure it out

SimpleXMLElement Object ( [resultset] => SimpleXMLElement Object ( [status] => Success [results] => 1 [totalResults] => 1 [currentPage] => 1 [totalPages] => 1 ) [items] => SimpleXMLElement Object ( [item] => SimpleXMLElement Object ( [identifiers] => SimpleXMLElement Object ( [isbn13] => 9783899735215 ) [url] => https://www.bookdepository.com/Crocodile-Newts-Axel-Hernandez/9783899735215 [biblio] => SimpleXMLElement Object ( [title] => Crocodile Newts [format] => Hardback ) [availability] => Available - dispatched from the UK in 4 business days [pricing] => SimpleXMLElement Object ( [price] => SimpleXMLElement Object ( [@attributes] => Array ( [currency] => GBP ) [selling] => 50.27 ) ) [contributors] => SimpleXMLElement Object ( [contributor] => SimpleXMLElement Object ( [name] => Axel Hernandez [roleDescription] => By (author) [url] => https://www.bookdepository.com/author/Axel-Hernandez ) ) ) ) )

Looks as though you need to expand

return $sxml->price; 

as your structure is more complex. Looks as though

return (string)$sxml->items->item->pricing->price->selling;

The cast to (string) makes the value easier to use elsewhere.