Discount on the first month

I would like to offer a discount coupon on the first month of a monthly subscription. I can’t find where. I can use a 30 day trial period that is the same price as the regular monthly payment, so that without a discount, the subscriber will pay the same thing as anyone else.

Is that the only way to apply a discount on the first month or is there something else?

https://www.ads-software.com/plugins/s2member/