How to add trial to stripe checkout using ASP.NET Core

Question

What is that syntax for adding a trial to asp core 3.1 using stripe checkout? I'm trying to assign TrialPeriodDays to SubscriptionData for a 7 day free trial.

// Checkout Session
var options = new SessionCreateOptions
                  {
                      LineItems = new List<SessionLineItemOptions>
                                  {
                                      new SessionLineItemOptions
                                          {
                                              Price = "price_1KJSMXC...",
                                              Quantity = 1,
                                          },
                                  },
                      // I believe I need to assign the trial to SubscriptionData below
                      SubscriptionData = { },           
                      Mode = "subscription",

                      SuccessUrl = "https://example.com/Success",
                      CancelUrl = "https://example.com/Cancel",
                  };