Best referral software

Happy new year all! I'd like to setup a referral offer for my members. "Refer a friend and get a free month" that sort of thing. A bit like Mubi's offer

https://mubi.com/referrals?lt=1vf5chykfkuu5aal4tb8dsejfp8rgvuyz7blq1z1610701213&utm_campaign=referral_introduction&utm_source=automation&utm_medium=email

Does anybody know the best bit of software/plugin/platform for handling this kind of functionality - haven't really seen any wordpress plugins that do it quite this way. I currently have a little wordpress site, but if there's a platform that has this functionality built-in, I'd consider it. Thanks everybody, all the best for 2021!