@Vaishali-Agarwal - Problem solved.

@Vaishali-Agarwal
You can see my previous version is working fine here - https://phpstack-378818-1259319.cloudwaysapps.com/

@Vaishali-Agarwal I tried but didn't find any issue. That's why I posted here with my source code.

@Vaishali-Agarwal I think there is no problem in Bagisto 1.2 . This error is showing only when I'm adding my payment package.

@Vaishali-Agarwal

If I remove my payment package the checkout works. But when I add again the error shows.

@Vaishali-Agarwal No

@Vaishali-Agarwal

Those changes are already there in my packages/Webkul/Checkout/src/Cart.php

private function linkAddresses(
        \Webkul\Checkout\Models\Cart $cart,
        array $billingAddressData,
        array $shippingAddressData
    ): void
    {
        $billingAddressModel = $cart->billing_address;
        if ($billingAddressModel) {
            $billingAddressData['address_type'] = CartAddress::ADDRESS_TYPE_BILLING;
            $this->cartAddressRepository->update($billingAddressData, $billingAddressModel->id);

            if ($cart->haveStockableItems()) {
                $shippingAddressModel = $cart->shipping_address;
                if ($shippingAddressModel) {
                    if (isset($billingAddressData['use_for_shipping']) && $billingAddressData['use_for_shipping']) {
                        $billingAddressData['address_type'] = CartAddress::ADDRESS_TYPE_SHIPPING;
                        $this->cartAddressRepository->update($billingAddressData, $shippingAddressModel->id);
                    } else {
                        $shippingAddressData['address_type'] = CartAddress::ADDRESS_TYPE_SHIPPING;
                        $this->cartAddressRepository->update($shippingAddressData, $shippingAddressModel->id);
                    }
                } else {
                    if (isset($billingAddressData['use_for_shipping']) && $billingAddressData['use_for_shipping']) {
                        $this->cartAddressRepository->create(array_merge($billingAddressData,
                            ['address_type' => CartAddress::ADDRESS_TYPE_SHIPPING]));
                    } else {
                        $this->cartAddressRepository->create(array_merge($shippingAddressData,
                            ['address_type' => CartAddress::ADDRESS_TYPE_SHIPPING]));
                    }
                }
            }
        } else {
            $this->cartAddressRepository->create(array_merge($billingAddressData, ['address_type' => CartAddress::ADDRESS_TYPE_BILLING]));

            if ($cart->haveStockableItems()) {
                if (isset($billingAddressData['use_for_shipping']) && $billingAddressData['use_for_shipping']) {
                    $this->cartAddressRepository->create(array_merge($billingAddressData, ['address_type' => CartAddress::ADDRESS_TYPE_SHIPPING]));
                } else {
                    $this->cartAddressRepository->create(array_merge($shippingAddressData, ['address_type' => CartAddress::ADDRESS_TYPE_SHIPPING]));
                }
            }
        }
    }

@Vaishali-Agarwal