Internal Server Error on Checkout

Hi,

I have WC Multivendor Marketplace and WC Multivendor Membership installed. I am also using WC subscriptions with their Stripe plugin. When a user goes to checkout they get an Internal Server Error above the form when submitting payment. If I disable WC Multivendor Marketplace the checkout works perfect and the order confirmation shows.

Here is my server log:

[28-Jan-2019 13:52:36 UTC] The WC_Cart::get_cart_url function is deprecated since version 2.5. Replace with wc_get_cart_url.
[28-Jan-2019 13:55:32 UTC] PHP Fatal error: Uncaught Error: Call to a member function trigger() on null in /home/ukmonthlysubscri/public_html/wp-content/plugins/wc-multivendor-marketplace/core/class-wcfmmp-commission.php:282
Stack trace:
#0 /home/ukmonthlysubscri/public_html/wp-includes/class-wp-hook.php(286): WCFMmp_Commission->wcfmmp_checkout_order_processed(1919, Array, Object(WC_Order))
#1 /home/ukmonthlysubscri/public_html/wp-includes/class-wp-hook.php(310): WP_Hook->apply_filters(NULL, Array)
#2 /home/ukmonthlysubscri/public_html/wp-includes/plugin.php(453): WP_Hook->do_action(Array)
#3 /home/ukmonthlysubscri/public_html/wp-content/plugins/woocommerce/includes/class-wc-checkout.php(1078): do_action(‘woocommerce_che…’, 1919, Array, Object(WC_Order))
#4 /home/ukmonthlysubscri/public_html/wp-content/plugins/woocommerce/includes/class-wc-ajax.php(434): WC_Checkout->process_checkout()
#5 /home/ukmonthlysubscri/public_html/wp-includes/class-wp-hook.php(286): WC_AJAX::checkout(”)
#6 /home/ukmonthlysubscri/public_html/wp-includes/class-wp-hook.php(310 in /home/ukmonthlysubscri/public_html/wp-content/plugins/wc-multivendor-marketplace/core/class-wcfmmp-commission.php on line 282

I don’t know what is causing this problem. I searched your forum for help and reinstalled but don’t think it is my PHP version, I’m using 7. Can you help?