Magento 1.9 – Observer After Payment Method Selection Before Order Placement

I've had a similar problem (removing dynamically payment methods) and solved it by extending the _canUseMethod($method) function in Mage_Checkout_Block_Onepage_Payment_Methods. There you can return false for specific payment methods which should not be shown in the payment selection.

Example:

class Company_Module_Block_Methods extends Mage_Checkout_Block_Onepage_Payment_Methods {
    protected function _canUseMethod($method) {
        if ($method != null && $method == 'checkmo') {
            $carriers = Mage::getSingleton('checkout/session')->getQuote()->getShippingAddress()->getShippingMethod();
            if ($carriers == 'flatrate_flatrate') {
                return parent::_canUseMethod($method);
            } else {
                return false;
            }
        }

        return parent::_canUseMethod($method);
    }
}

The config XML would look like:

<config>
    <global>
        <blocks>
            <checkout>
                <rewrite>
                    <onepage_payment_methods>Company_Module_Block_Methods</onepage_payment_methods>
                </rewrite>
            </checkout>
        </blocks>
    </global>
</config>

That way I could remove payment methods right before they get shown in the one page checkout.

Hope that helps anyone.

You should use redirectAfterPlaceOrder: false in defaults, then the afterPlaceOrder function redirection will start working. Refer this sample code

 define(
    [
        'jquery',
        'Magento_Checkout/js/view/payment/default',
        'mage/url',
        'Magento_Checkout/js/action/place-order'
    ],
    function ($,Component,url,placeOrderAction) {
        'use strict';

        return Component.extend({
            defaults: {
                redirectAfterPlaceOrder: false
            },

            afterPlaceOrder: function (data, event) {
                 window.location.replace(url.build('yourmodule/namespace/controller'));

            }

        });
    }
);