Activation Error

Hi!

Im using the plugin Join My Multisite, and I have tried to use two shortcode [join-my-multisite] and [join-this-site], but Its not working to activate a user, with the activation link.

I get this error:
Notice: Trying to get property of non-object in /var/www/html/wordpress/wp-content/themes/mytheme/functions.php on line 660

Fatal error: Call to a member function get_cart_url() on a non-object in /var/www/html/wordpress/wp-content/themes/mytheme/functions.php on line 660

The only thing I can see on that line is:
$cart_url = $woocommerce->cart->get_cart_url();

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Thanks

https://www.ads-software.com/plugins/join-my-multisite/