Magento – Module for Accepting Payments via Google Checkout

At last i was able to figure out how to do it. Thought to share the answer so someone like me can save the time and spend it for some fruitful purpose :P

So, what i did was

1) I checked for PayPal's API Calls from developer profile. The link for it is PayPal API

To open the credit card option by default you need to pass the API with parameters LANDINGPAGE=Billing.

2) Searched for API calls in Magento for PayPal and found the file Nvp.php at app/code/core/Mage/Paypal/Model/Api/Nvp.php

3) Search for the function callSetExpressCheckout() after $this->_exportLineItems($request); enter the following line $request['LANDINGPAGE'] = 'Billing';

This is all. Now test it using Express Checkout. I haven't yet tested it thorougly. Please add up to the answer if there are any better suggestion for it.

Theres a really handy event for disabling and enabling payment methods on the fly.

Add the following into your config.xml section

<payment_method_is_active>
    <observers>
        <preorder_payment>
            <class>your_module/observers</class>
            <method>invoiceOnly</method>
        </preorder_payment>
    </observers>
</payment_method_is_active>

Then create the following function in your observer.php

/**
 * Disable all other payments
 * @param Varien_Event_Observer $observer
 */
public function invoiceOnly(Varien_Event_Observer $observer) {

    $_result = $observer->getResult();
    $_methodInstance = $observer->getMethodInstance();

    if(BILLING_CONDITION_HERE) {
        if($_methodInstance->getCode() != 'METHOD_CODE') {
            $_result->isAvailable = false;
        } else {
            $_result->isAvailable = true;
        }
    }

}

You'll need to modify the BILLING_CONDITION_HERE and the METHOD_CODE (to the invoice payment method code)

This will automatically disable everything except METHOD_CODE if the billing condition is met.