Openpay LIBRARY

The problem that I have now it's when I call any of the class/method like:

$customer = $openpay->customers->add($customerData);
$charge = $openpay->charges->create($chargeData);

I get the following error:
Call to undefined method stdClass::create()
Call to undefined method stdClass::add()

I don't know why I'm getting this error and how to fix it.
Do you have an idea what I'm doing wrong or what I need to change?
Thanks for your help.

Looks like the $openpay variable is not initialized to an openpay class.
Have you created the $openpay object? From the docs:

PHP Code:

$openpay = Openpay::getInstance('MERCHANT_ID', 'PRIVATE_KEY', 'COUNTRY_CODE');