convert curl to guzzle for spreedly API

I'm trying to convert this curl call to guzzle:

curl https://core.spreedly.com/v1/gateways/CAL6uXHtGfDsxV2kW6apTP5JhG/purchase.xml \
-u 'Ll6fAtoVY5hTGlJEmtpo5YTS:RKOCG5D8jhgfdDSg524u5iF22XD4Io5VXmyzdCptrvHFTTSy' \
-H 'Content-Type: application/xml' \
-d '<transaction>
      <payment_method_token>ZgPNHes541EMlBN86glRDKRexzq</payment_method_token>
      <amount>100</amount>
      <currency_code>USD</currency_code>
    </transaction>'

I'm know use this so much so any help will be appreciated

This is what I've tried, but I always get this error "Client error response [status code] 422 [reason phrase] Unprocessable Entity"

$xml =  '<transaction>\n';
$xml .=     '<payment_method_token>$payment_method_token</payment_method_token>\n';
$xml .=     '<amount>100</amount>\n';
$xml .=     '<currency_code>USD</currency_code>\n'
$xml .= '<transaction>\n';
$headers = ['Content-Type' => 'application/xml', 'auth' => ['Ll6fAtoVY5hTGlJEmtpo5YTS', 'RKOCG5D8jhgfdDSg524u5iF22XD4Io5VXmyzdCptrvHFTTSy']];
$client = new Client('https://core.spreedly.com/v1/gateways/CAL6uXHtGfDsxV2kW6apTP5JhG/purchase.xml');
$requestCurl = $client->post('', $headers, $xml,[]);
$response = $requestCurl->send()->xml();
dd($response);

Thanks!

It should look something like this:

$client = new Client('https://core.spreedly.com/v1/gateways/merchant_id');

$xml = '<...>';
$options = [
    'headers'   => [ 'Content-Type' => 'application/xml' ],
    'auth'      => ['username', 'password'],
    'body'      => $xml,
];

$response = $client->post('/purchase.xml', $options);

and you might want to take another look at your code and figure out if you've accidentally posted your API credentials publicly.