In-app purchase. Unable to buy again. Item response: "7 Item Already Owned"

I'm figuring in this problem when I try to by for the second time the same consumable. First time work perfectly but i can't buy it again. I'm testing billing and I don't pay real but I'm using test card. could Anyone help me to solve the problem ? Thanks

Here my code:

private fun setupBillingClient() {
    billingClient = BillingClient.newBuilder(Dodgers.context!!)
        .enablePendingPurchases()
        .setListener(this@ShopFragment)
        .build()
    billingClient.startConnection(object : BillingClientStateListener {
        override fun onBillingSetupFinished(billingResult: BillingResult) {
            if (billingResult.responseCode == BillingClient.BillingResponseCode.OK) {
                // The BillingClient is setup successfully
                loadAllSKUs()
            }
        }

        override fun onBillingServiceDisconnected() {
            // Try to restart the connection on the next request to
            // Google Play by calling the startConnection() method.
            Log.e("billing", "error")
        }
    })
}

    private fun loadAllSKUs() = if (billingClient.isReady) {
    val params = SkuDetailsParams
        .newBuilder()
        .setSkusList(skuList)
        .setType(BillingClient.SkuType.INAPP)
        .build()
    billingClient.querySkuDetailsAsync(params) { billingResult, skuDetailsList ->
        // Process the result.
        if (billingResult.responseCode == BillingClient.BillingResponseCode.OK && skuDetailsList!!.isNotEmpty()) {
            this.skuDetailsList = skuDetailsList
        }
    }
} else {
    println("Billing Client not ready")
}

ONCLICK ITEM:

private fun startBillingAction(shop: Shop) {
    if (skuDetailsList.isNotEmpty()) {
        val skuDetails = skuDetailsList.first { it.sku == shop.sku }
        val billingFlowParams = BillingFlowParams
            .newBuilder()
            .setSkuDetails(skuDetails)
            .build()
        billingClient.launchBillingFlow(requireActivity(), billingFlowParams)
    } else {
        showSnackBar(shop.unit)
    }
}

    override fun onPurchasesUpdated(
    billingResult: BillingResult,
    purchases: MutableList<Purchase>?
) {
    if (billingResult.responseCode == BillingClient.BillingResponseCode.OK && purchases != null) {
        for (purchase in purchases) {
            acknowledgePurchase(purchase.purchaseToken, purchase.sku) <==================== HERE FIRST TIME
        }
    } else if (billingResult.responseCode == BillingClient.BillingResponseCode.USER_CANCELED) {
        // Handle an error caused by a user cancelling the purchase flow.
        Log.e("billing", "error")
    } else {
        // Handle any other error codes.
        Log.e("billing", "error") <==================== HERE SECOND TIME WITH RESPONCE CODE 7
    }
}

    private fun acknowledgePurchase(purchaseToken: String, sku: String) {
    val params = AcknowledgePurchaseParams.newBuilder()
        .setPurchaseToken(purchaseToken)
        .build()
    billingClient.acknowledgePurchase(params) { billingResult ->
        val responseCode = billingResult.responseCode
        val debugMessage = billingResult.debugMessage

        //STUFF IF CORRECT
    }
}

I've 6 items. I can buy correctly every items first time but if I try to by again I've always the same problem and documentation doesn't help!

EDIT:

Following suggestion, i need to consume item. So I must modify acknowledgePurchase function as:

private fun acknowledgePurchase(purchase: Purchase, sku: String) {
    val params = AcknowledgePurchaseParams.newBuilder()
        .setPurchaseToken(purchase.purchaseToken)
        .build()
    billingClient.acknowledgePurchase(params) { billingResult ->
        val responseCode = billingResult.responseCode
        val debugMessage = billingResult.debugMessage

        CoroutineScope(Dispatchers.Main + exceptionHandler).launch {
            val gemItem = Gem.values().find { it.sku == sku }
            DataManager.instance.user.value!!.gems += gemItem!!.reward
            // TODO add gem animations
            gem_value.text = DataManager.instance.user.value!!.gems.toString()
        }

        // Verify the purchase.
        // Ensure entitlement was not already granted for this purchaseToken.
        // Grant entitlement to the user.
        val consumeParams =
            ConsumeParams.newBuilder()
                .setPurchaseToken(purchase.purchaseToken)
                .build()

        billingClient.consumeAsync(consumeParams) { billingResult, outToken ->
            if (billingResult.responseCode == BillingClient.BillingResponseCode.OK) {
                // Handle the success of the consume operation.
                LogHelper.log(TAG, "Item Consumed!!!")
            }
        }
    }
}

And that's it :-). Thanks!!!

After buying an item you should consume it to enable purchase available again