Creating a free membership with a trial period (Limited-time free membership) [OptimizeMember]

This can be done using PayPal Pro Forms or Membership Order Button element. To do this, you just need to set 0 as the initial payment and set the trial date (no. of days access).

Please check also this article for some important notes:
https://help.optimizepress.com/article/322-paypal-free-trial-auto-return