coupon code for three months membership's plan

Hello
I have an issue:
I want to create a coupon code that I can give to some friends of mine so they can register on the recurrent membership’s plan of three months but with the first three months free thanks to the coupon code ! (the validation of the payement after registration is done by stripe )
So if you see on my website (you have all you need in this conversation) the recurrent plan of three months has a price of 59 euros so maybe a coupon code that gives “-59 euros” so they can register with the first three months free of this recurrent membership’s plan !
Can you tell me how to do that please ??
Or an alternative with the same results I don’t know please help me
link of website : https://beantic.com/my-account/
I can send you in private all the logins and passwords you need 🙂 if needed

Good to you;