Magento 1.8 – PayPal Payment Standard Method Not Visible

The action for this form is set in the file Mage_Paypal_Block_Standard_Redirect::_toHtml. Here the form is created and the action is added via the following snippet:

$form->setAction($standard->getConfig()->getPaypalUrl())
    ->setId('paypal_standard_checkout')
    ->setName('paypal_standard_checkout')
    ->setMethod('POST')
    ->setUseContainer(true);

The function for getting the path to paypal will simply perform a sprintf and replace some items based on if you are using the sandbox or if you are passing in parameters.

public function getPaypalUrl(array $params = array())
{
    return sprintf('https://www.%spaypal.com/webscr%s',
        $this->sandboxFlag ? 'sandbox.' : '',
        $params ? '?' . http_build_query($params) : ''
    );
}

It appears that in newer versions of Magento this url has been changed, in Mage 1.9 the functions looks as follows.

public function getPaypalUrl(array $params = array())
{
    return sprintf('https://www.%spaypal.com/cgi-bin/webscr%s',
        $this->sandboxFlag ? 'sandbox.' : '',
        $params ? '?' . http_build_query($params) : ''
    );
}

What I would do firstly is try updating your system to use the url https://www.%spaypal.com/cgi-bin/webscr%s to see if that works.

You need to tell PayPal about the discount order total. You can do this by modifying the PayPal cart object that is passed.

Observe the event paypal_prepare_line_items (Mage_Paypal_Model_Cart line 318)

In your observer, you load the paypal cart as such:

$payPalCart = $observer->getPaypalCart();

Get your discount amount from the order

$order = $payPalCart->getSalesEntity();
$discountAmount = $order->getDiscountAmount();

You can then set the discount amount by calling updateTotal()

$payPalCart->updateTotal(Mage_Paypal_Model_Cart::TOTAL_DISCOUNT, $discountAmount);

And that is it, PayPal will now know about your discount. This should work for standard, advanced, and pro I believe - both express checkout and direct payments.