Critical error when changing orders from Processing to Completed

This morning I was processing my orders and using the bulk feature to change them from Processing to Completed when I received this error:

“There has been a critical error on this website. Please check your site admin email inbox for instructions.”

I have not received this error before. I then received this email:

When seeking help with this issue, you may be asked for some of the following information:
WordPress version 5.9.1
Current theme: Sinatra (version 1.2.1)
Current plugin: Creative Mail by Constant Contact (version 1.5.0)
PHP version 8.0.16

Error Details
=============
An error of type E_ERROR was caused in line 810 of the file /home2/sarakeps/public_html/wp-content/plugins/creative-mail-by-constant-contact/src/Managers/CheckoutManager.php. Error message: Uncaught Error: Attempt to modify property "billing" on null in /home2/sarakeps/public_html/wp-content/plugins/creative-mail-by-constant-contact/src/Managers/CheckoutManager.php:810
Stack trace:
#0 /home2/sarakeps/public_html/wp-includes/class-wp-hook.php(309): CreativeMail\Managers\CheckoutManager->order_completed_trigger_wc_hook(7471)
#1 /home2/sarakeps/public_html/wp-includes/class-wp-hook.php(331): WP_Hook->apply_filters(NULL, Array)
#2 /home2/sarakeps/public_html/wp-includes/plugin.php(474): WP_Hook->do_action(Array)
#3 /home2/sarakeps/public_html/wp-content/plugins/woocommerce/includes/class-wc-order.php(364): do_action('woocommerce_ord...', 7471, Object(Automattic\WooCommerce\Admin\Overrides\Order))
#4 /home2/sarakeps/public_html/wp-content/plugins/woocommerce/includes/class-wc-order.php(222): WC_Order->status_transition()
#5 /home2/sarakeps/public_html/wp-content/plugins/woocommerce/includes/class-wc-order.php(334): WC_Order->save()
#6 /home2/sarakeps/public_html/wp-content/plugins/woocommerce/includes/admin/list-tables/class-wc-admin-list-table-orders.php(684): WC_Order->update_status('completed', 'Order status ch...', true)
#7 /home2/sarakeps/public_html/wp-includes/class-wp-hook.php(307): WC_Admin_List_Table_Orders->handle_bulk_actions('/wp-admin/edit....', 'mark_completed', Array)
#8 /home2/sarakeps/public_html/wp-includes/plugin.php(189): WP_Hook->apply_filters('/wp-admin/edit....', Array)
#9 /home2/sarakeps/public_html/wp-admin/edit.php(212): apply_filters('handle_bulk_act...', '/wp-admin/edit....', 'mark_completed', Array)
#10 {main}
  thrown

I need to make sure that payment is going to go through and if emails will be sent. Thank you for any urgent help you can provide.

The page I need help with: [log in to see the link]