Eshop Customs Gateway

I m trying to develop a merchant gateway pluggin for eshop using the skeleton code provided here
http://quirm.net/wiki/eshop/additional-plugins-and-code-snippets/adding-a-merchant-gateway/
I m able to add some code and get past couple of screen but when i reach
http://192.168.100.100/shopping-cart/checkout/?eshopaction=redirect It fails.

The error log indicates that that it fails here
PHP message: PHP Fatal error: require_once(): Failed opening required ‘/vagrant/wordpress/wp-content/plugins/eshop/extra.php’ (include_path=’.:/usr/share/php:/usr/share/pear’) in /vagrant/wordpress/wp-content/plugins/eshop/cart-functions.php on line 2535″ while reading response header from upstream, client: 192.168.100.1, server: localhost, request: “POST /shopping-cart/checkout/?eshopaction=redirect HTTP/1.1”, upstream: “fastcgi://127.0.0.1:9000”, host: “192.168.100.100”, referrer: “http://192.168.100.100/shopping-cart/checkout/”

I checked the relevent code and it seems it is looking for a function

$eshop_order_function = ‘eshop_’ . $paymentmethod.’_redirect’;
if(function_exists($eshop_order_function)){
$espost = $eshop_order_function($espost);
}elseif(preg_match(‘/^([a-zA-Z0-9_\-]+)$/’, $paymentmethod)){
require_once(dirname(__FILE__) . ‘/’ . $paymentmethod . ‘.php’);
}

Does this pluggin code is current or do i need to make any changes

https://wordpress.org/plugins/eshop/