Razorpay has hidden the email address field during checkout. If you are using the single-click checkout feature, you need to change this setting from the Razorpay dashboard. 

Email address is needed to assign the course after purchase.

Please make the email address a mandatory field during checkout. Click here for step by step process - https://razorpay.com/docs/payments/dashboard/settings/configuration/#configure-email-address-field