async getPriceForTier(tierSlug, cadence) {
        const product = await models.Product.findOne({slug: tierSlug});

        if (!product) {
            throw new Error('Product not found with slug ' + tierSlug);
        }
        const tier = await tiers.api.read(product.id);
        const payments = members.api.paymentsService;
        const {id} = await payments.createPriceForTierCadence(tier, cadence);
        return this.#getData(this.prices, id)[1];
    }
Fetches a mock Stripe price for a given product/tier (by slug).
@param {string} tierSlug
@param {'month' | 'year'} cadence
@returns {Promise<object>} - The fetched Stripe price object.