In the subscription question's configuration, click plans under Available Plans to add plans or click plans under Selected Plans to remove plans.

Plans are pulled from the pricing plans set up on Stripe or Braintree directly. The mode (live or test) you choose on your form must match the mode you created the pricing plan in on Stripe or the plan will not appear for selection.

NOTE: Subscription plan prices will not show in the form or check-out total price.
Instead, the subscription plan price will be referred to in the message below the check-out total.
E.g
You will be subscribed to:
TEST SUBSCRIPTION ($10.00 / month).