Order Cancellation link missing key

I am using woocommerce to sell services as a product. I am using it for appointment booking system. i needed the wc cancel order plugin for cancelling the appointment. i am making use of guest feature provided by the plugin. the problem is that when the user recieves the mail, the cancellation link is there but it is missing the key. that’s why when the user clicks on that link, a blank page appears.

here is the link that appears: http://13.200.167.217/wordpress/guest-cancel-req/?key=

please help me resolve this issue. tell me what i can do?