WooCommerce Subscriptions - apply coupons on next renewal
Refer a friend is compatible with the WooCommerce Subscriptions plugin.
To make it work, after setting up plugin per the step by step guide that you can find on this link., you need to enable woocommerce subscription option under plugins general settings and that's it, coupons will be automatically applied to customers on their next payment.
So, once your customer has referred a friend to your store and earned a coupon, that coupon value will be automatically deducted from his next renewal. If the amount of coupon equals the subscription price, his renewal will be free. Giving 1 free month(or whatever subscription period you have) in exchange for getting a new person signed up is a great way to increase your site subscription base.
This feature works with payment gateways that support recurring total modifications. Read more about them here: https://docs.woocommerce.com/document/subscriptions/payment-gateways/#advanced-features