public function applyCoupon($coupon, $removeOthers = false)
{
if (!$this->active()) {
throw new InvalidArgumentException("Unable to apply coupon. Subscription not active.");
}
BraintreeSubscription::update($this->braintree_id, ['discounts' => ['add' => [['inheritedFromId' => $coupon]], 'remove' => $removeOthers ? $this->currentDiscounts() : []]]);
}