Failed to parse integer value

I’m trying to use this plugin with some custom code and receiving the error
"Uncaught Failed to parse XML-RPC request: Failed to parse integer value: 1234567890123456"
while trying to create a credit card. Has anyone else experienced this? I’m using the example code from the SDK github

$creditCard = new Infusionsoft_CreditCard();
$creditCard->ContactId = $contact->Id;
$creditCard->BillName = $contact->FirstName . ' ' . $contact->LastName;
$creditCard->FirstName = $contact->FirstName;
$creditCard->LastName = $contact->LastName;
$creditCard->CardNumber = 1234567890123456;
$creditCard->CVV2 = 197;
$creditCard->CardType = 'Visa';
$creditCard->Status = 3; //0: Unknown, 1: Invalid, 2: Deleted, 3: Valid/Good, 4: Inactive
$creditCard->save();