Try before you subscribe
This is an example of how a "First month free" might work. It could be first month free, first month half price, $20 off the first monty only, or any discount you want!
Click the link below to try it out! Add a subscription to your cart and you'll notice in the checkout the discount code is automatically applied. When you get to the last step on the payments screen it shows that the recurring charge will be $17.99 a month after the first month.
The discount code only works on the first month of this specific subscription, for this specific product, and only once per customer. Customers are not able to copy the code and use it again, or for for any other product.
They still have to enter their credit card info, but with the discount code in this example the first month will be free. After the first month regular billing will begin.