Creates a subscription that bills a customer on a recurring cadence, in the live or test mode of the API key used. Each item defines its price through price_data, referencing an existing product (product) or defining one inline (product_data). All items must share a compatible currency (CLF items bill alongside CLP) and the same recurring interval and interval_count. A subscription can have up to 10 items. Fintoc charges each subscription automatically using payment_method, so the collection_method is always charge_automatically. Without trial_end, Fintoc sets the billing_cycle_anchor to the creation time and finalizes an initial invoice immediately. The subscription starts incomplete and becomes active once that first payment succeeds. For a zero-amount subscription, Fintoc marks the initial invoice paid and the subscription starts active. With trial_end, the subscription's status is trialing. Fintoc sets the billing_cycle_anchor to the trial end and generates the first invoice when the trial ends.