docs: New IAB "prorates" feature

try your subscription content before buying it. The trial period runs for the

period of time that you set and then automatically converts to a full

subscription managed according to the subscription's billing interval and

price. Free trials are supported for monthly and annual subscriptions only, and

are not supported for seasonal subscriptions.</p>

price. Google Play supports free trials for all subscription types, including

seasonal subscriptions.</p>

<p>To take advantage of a free trial, a user must "purchase" the full

subscription through the standard In-app Billing flow, providing a valid form of

the amount set

for the full subscription, and continuing at the subscription interval. If

necessary, the user can cancel the subscription at any time during the trial

period. In this case, Google Play <em>marks the subscription as expired immediately</em>,

rather than waiting until the end of the trial period. The user has not

paid for the trial period and so is not entitled to continued access after

cancellation.</p>

period. In this case, the subscription remains active until the end of the

trial period, but Google Play sets the subscription <em>not</em> to renew

automatically; at the end of the trial period the subscription expires, and

Google Play does not charge the user.</p>

<p>You can set up a trial period for a subscription in the Developer Console,

without needing to modify or update your APK. Just locate and edit the

product from the product list offered in your app to prevent users from seeing

or purchasing it.</p>

<h3 id="prorate">Prorated Seasonal Subscription Prices</h3>

<p>You can set up prorated prices for users who buy seasonal subscriptions

after the season's start date. You specify the date on which the discounted

price takes effect. The discounted price takes effect at 0:00 UTC on

the specified date. You can set multiple prorated prices, dropping the

subscription price lower and lower as the season goes on. If a user purchases

a prorated seasonal subscription and remains subscribed until the start of the

next season, Google Play charges them the full subscription price when the next

season starts.</p>

<p>For example, the professional checkers season runs from March 1 to August 31.

The <em>Checkers Dilettante</em> app offers a seasonal subscription for €10. The

app also offers two prorated prices: €7.50 for users who sign up on or after

June 1, and €5 for users who sign up on or after

August 15. Regardless of when the user signs up, the seasonal subscription ends

on August 31.</p>

<h2 id="cancellation">Subscription Cancellation</h2>

<p>Users can view the status of all of their subscriptions and cancel them if

<div class="sidebox">

  <h2><strong>New in In-App Billing</strong></h2>

  <ul>

  <li><strong>Prorated Subscription Prices</strong>&mdash;Content providers can

    lower the price of seasonal subscriptions for users who sign up late in the

    season. For example, a sports-related service might lower the subscription

    price halfway through the sport's season.</li>

  <li><strong>Free Trials</strong>&mdash;Content providers can

    offer free trial periods for all kinds of subscriptions, including

    seasonal subscriptions. If a user cancels the subscription in the trial

    period, they pay nothing. If they do not cancel by the end of the

    trial period, the subscription automatically converts to a paid

    subscription.</li>

  <li><strong>Subscription Upgrade/Downgrade</strong>&mdash;A user can

    subscribe to a higher or lower tier of subscription while their current

    subscription is active. The old subscription is canceled, and the unused