Luminary requires a valid payment method to begin a free trial for the following reasons:
1. This allows us to confirm your eligibility for the Premium subscription.
2. You can continue to enjoy Luminary Premium after your trial period ends without interruption.
If your account is canceled during the free trial period you will not be renewed on your renewal date and will not be charged. For more information about this, check out these articles:
How do I check my account status?
How do I cancel my Luminary Premium subscription?