Unable to upgrade/downgrade android subscription using in_app_purchase flutter

Question

I am fetching past purchase details and as mentioned in the documentation I am providing the fetched details to ChangeSubscriptionParam with required ProationMode.

However I am getting error in playstore modal as Something went wrong on our end. Please try again, and the debug console says Activity finished with resultCode 0 and billing's responseCode: 5.

This is the code I am using :

final platform = iapConnection
            .getPlatformAddition<InAppPurchaseAndroidPlatformAddition>();
        final pastPurchases = await platform.queryPastPurchases();

        GooglePlayPurchaseDetails? oldPurchaseDetails;

        // Assumes 1 or none active purchase.
        for (var purchase in pastPurchases.pastPurchases) {
          oldPurchaseDetails = purchase;
        }

        final purchaseParam = GooglePlayPurchaseParam(
            productDetails: event.productDetails,
            changeSubscriptionParam: oldPurchaseDetails != null
                ? ChangeSubscriptionParam(
                    oldPurchaseDetails: oldPurchaseDetails,
                    prorationMode: ProrationMode.deferred)
                : null);

        await iapConnection.buyNonConsumable(purchaseParam: purchaseParam);

Answer 1

I figured out the reason for my error. So I was trying subscription model in India and had 3 subscription model set up however 2 of them were priced above 5000 because of which they were being treated as prepaid plan (India's Subscription Rules). And according to documentation When upgrading, downgrading to a prepaid plan from auto-renewing plan, the only allowed proration mode is IMMEDIATE_AND_CHARGE_FULL_PRICE and I was aiming for DEFERED proration mode, hence the error.