Glad to see the beta release of official InApp purchase plugin. Please add support for upgrading/downgrading subscription plans. Currently, the plugin does not support this. In Android, this can be achieved by passing an old SkuId while purchasing a new plan.
Reference: https://developer.android.com/google/play/billing/billing_subscriptions#Allow-upgrade
Version: in_app_purchase: ^0.1.0
@mklim