Some undefined function is causing IPN errors, need fix/patch please

There isnt a cart page. The main shop page is http://www.hopeforthree.org/shop43

I just installed it from the wordpress.org repo.

Here is the function the error is referring to:

// Start of IPN handling (script execution)
function wpc_handle_paypal_ipn()
{
    $debug_log = "ipn_handle_debug.log"; // Debug log file name
    $ipn_handler_instance = new paypal_ipn_handler();

    $debug_enabled = false;
    $debug = get_option('wp_shopping_cart_enable_debug');
    if ($debug){
        $debug_enabled = true;
    }

    if ($debug_enabled)
    {
        echo 'Debug is enabled. Check the '.$debug_log.' file for debug output.';
        $ipn_handler_instance->ipn_log = true;
        //$ipn_handler_instance->ipn_log_file = realpath(dirname(__FILE__)).'/'.$debug_log;
    }
    $sandbox = get_option('wp_shopping_cart_enable_sandbox');
    if ($sandbox) // Enable sandbox testing
    {
        $ipn_handler_instance->paypal_url = 'https://www.sandbox.paypal.com/cgi-bin/webscr';
        $ipn_handler_instance->sandbox_mode = true;
    }
    $ipn_handler_instance->debug_log('Paypal Class Initiated by '.$_SERVER['REMOTE_ADDR'],true);
    // Validate the IPN
    if ($ipn_handler_instance->validate_ipn())
    {
        $ipn_handler_instance->debug_log('Creating product Information to send.',true);
        if(!$ipn_handler_instance->validate_and_dispatch_product())
        {
            $ipn_handler_instance->debug_log('IPN product validation failed.',false);
        }
    }
    $ipn_handler_instance->debug_log('Paypal class finished.',true,true);
}

Do you see anything wrong??

I tried the PayPal’s IPN simulator but its showing “We could not send an IPN due to an http error.”

Sorry about my absence.
Is the ipn listener http://www.hopeforthree.org/?simple_cart_ipn=1 ?
Im getting an error, if you stop the page from redirecting to paypal and look at the details you’ll see whats going on.
Ive enabled and disabled IPN on paypal with the notification url set to http://www.hopeforthree.org and http://www.hopeforthree.org/?simple_cart_ipn=1
Neither setting made a difference.

The cart works fine, thanks. But that error keeps being emailed.

Yea, I updated to 4.1.4. Is the ipn listener http://www.hopeforthree.org/?simple_cart_ipn=1 ?

Yes the link will take you to paypal, but a email keeps being sent

Please check your server that handles PayPal Instant Payment Notification (IPN) messages. Messages sent to the following URL(s) are not being received:

http://www.hopeforthree.org/?simple_cart_ipn=1

If you do not recognize this URL, you may be using a service provider that is using IPN on your behalf. Please contact your service provider with the above information.

Once you or your service provider fix this problem, you or your service provider can resend the failed messages from the IPN History page. If this problem continues, PayPal may disable the IPN feature for your account.

Thank you for your prompt attention to this issue.

Thanks,
PayPal

The error on the page says

Fatal Error (hide details) (remove)
The site encountered a problem that it cannot recover from. Please use the following information to try to resolve the problem.

Error Message

Fatal Error: Call to undefined function wpc_handle_paypal_ipn() in /var/www/vhosts/hopeforthree.org/httpdocs/wp-content/plugins/wordpress-simple-paypal-shopping-cart/wp_shopping_cart_misc_functions.php on line 19
Description

The WP Simple Paypal Shopping cart plugin code created an error that caused PHP execution to fail.

The code tried to run a function that doesn’t exist (wpc_handle_paypal_ipn()). This type of error is typically caused by a simple typo (is_hom() rather than is_home()), by calling a function provided by a plugin when that plugin is not activated, by calling a function before it is ready (such as calling a function before the code that creates it has run), or by using a function that no longer exists (the function may have been removed from WordPress core or the plugin/theme that previously supplied it).

Solutions

Invalid code modifications can cause this problem. If you have made any modifications to the plugin, remove them and try to load the site again.
It is possible that this plugin’s code is out of date and that an upgrade is available. Check with the plugin’s author to see if an upgrade is available.
There may be a conflict with another plugin running on the site. Try upgrading the other plugins on the site. A plugin conflict can be ruled out by deactivating all the other active plugins on the site and checking to see if the error still occurs.
The WP Simple Paypal Shopping cart plugin may not have been fully uploaded. Uploading the plugin again could fix the issue. Important: If you do this, you will lose any modifications made to the plugin.
Error Source Details

Type Plugin
Name WP Simple Paypal Shopping cart
Version 4.1.4
Author Tips and Tricks HQ, Ruhul Amin
Path /var/www/vhosts/hopeforthree.org/httpdocs/wp-content/plugins/wordpress-simple-paypal-shopping-cart
File wp_shopping_cart_misc_functions.php
Other Software Details

WordPress Version 4.3.1
PHP Version 5.3.3
Full Error Details

Type Fatal Error (E_ERROR)
Message Call to undefined function wpc_handle_paypal_ipn()
File /var/www/vhosts/hopeforthree.org/httpdocs/wp-content/plugins/wordpress-simple-paypal-shopping-cart/wp_shopping_cart_misc_functions.php
Line 19
Type Description This type of error indicates that PHP cannot continue to run the code. Typical causes of this type of error are code bugs that have typos, missing or incomplete files (such as a file that was only partially uploaded), and the code using more memory than it is allowed.