Yep! Only Burpple Beyond members on an active plan can refer friends.
To qualify for the referral reward, do make sure that your membership plan is active at the time of referral activation. Should you opt to cancel your membership's auto-renewal, note that your free month(s) will be forfeited, if any.
For the special Referral Campaign between 15 Oct and 15 Nov 2019, only members on an active annual Premium plan can refer friends.