Whoever got or initially got that promo code, got it by signing up to their referral program, as we all into internet marketing know that promo codes are given only to those who sign up for referral programs. So, it is : use the promo code to get 1 month free and after the 1 month if anyone goes for paid plan, then the person who initially got this promo code, will obviously get his or her referral commissions.
Ofcourse, OP has not directly got the promo code from the platform, but whoever got it by signing up for their referral program would end up getting referral commissions when anyone uses this promo code takes up their paid plan at the end of the 1 month free. Marvels of internet marketing.
OP, thanks for sharing the promo code and please do keep sharing with us similar promo codes.