async removeCouponFromSubscription(id) {
        await this._rateLimitBucket.throttle();
        const subscription = await this._stripe.subscriptions.update(id, {
            coupon: ''
        });
        return subscription;
    }
Remove the coupon from the Stripe Subscription by ID.

@param {string} id - The ID of the subscription to remove coupon from

@returns {Promise<ISubscription>}