in onPurchasesUpdated, how to get accountid which was setted in BillingFlowParams

I am using com.android.billingclient:billing:1.1 for android's in app billing. I start pay in below code:

BillingFlowParams flowParams = BillingFlowParams.newBuilder()
                            .setSku(productId)
                            .setType(BillingClient.SkuType.INAPP)
                            .setAccountId(accountId)
                            .build();
billingClient.launchBillingFlow(this, flowParams);

It will callback on:

void onPurchasesUpdated(@BillingResponse int responseCode, @Nullable List<Purchase> purchases);

The question is how to get account which was seated in BillingFlowParams?

from in onPurchasesUpdated, how to get accountid which was setted in BillingFlowParams