Begins the purchase flow for a specific product.
It makes an async call to the API, so the result isn't available immediately.
If they are successfully subscribed this plugin will emit the
purchase event along
with the purchase data.
If they cannot, i.e. it's not in the list of supported APIs, or the request
was rejected, it will emit a
purchasefail event instead.
The identifier of the product to purchase.
An optional developer-specified payload, to be included in the returned purchase's signed request.
This Facebook Instant Games Plugin instance.