How to Validate Blockchain Networks in a Crypto Payment Application Using C#

When working with crypto payments, one issue that can easily be overlooked is the blockchain network.

A user may have the correct token but select the wrong network while making a payment. For example, USDT can exist on multiple networks, but a payment application may support only a specific set of them. If the application does not validate the selected network properly, the payment can fail or the funds can end up being sent through an unsupported network.

I faced this kind of problem while thinking about how a crypto payment system should handle network selection. The basic idea is actually quite simple: don't process a payment until you know that both the asset and the selected network are supported.

Let's see how we can handle this using C#.

First, Define the Supported Networks

Instead of keeping network names as random strings throughout the application, I prefer keeping them in one place.

For example:

public enum PaymentNetwork
{
    Polygon,
    ArbitrumOne,
    BnbSmartChain
}

Now the application has a clear list of networks it understands.

If another network needs to be added later, it can be added here instead of changing network names in multiple places.

Checking Whether a Network Is Supported

We can create a small method that checks whether the selected network is one of the networks supported by the application.

public bool IsSupportedNetwork(PaymentNetwork network)
{
    return network == PaymentNetwork.Polygon ||
           network == PaymentNetwork.ArbitrumOne ||
           network == PaymentNetwork.BnbSmartChain;
}

Then, before processing a payment:

if (!IsSupportedNetwork(selectedNetwork))
{
    throw new InvalidOperationException(
        "The selected blockchain network is not supported."
    );
}

This is a simple check, but it prevents the application from blindly accepting a network that it cannot actually process.

Network and Token Should Be Validated Together

There is another thing worth considering.

Checking only the network may not be enough. A payment system usually needs to know which token is being used on which network.

For example, the application might support USDT on Polygon but have different rules for another asset.

We can represent this relationship with a small model:

public class SupportedPayment
{
    public string Asset { get; set; }
    public PaymentNetwork Network { get; set; }
}

Then we can define the combinations supported by the application:

var supportedPayments = new List<SupportedPayment>
{
    new SupportedPayment
    {
        Asset = "USDT",
        Network = PaymentNetwork.Polygon
    },
    new SupportedPayment
    {
        Asset = "USDT",
        Network = PaymentNetwork.ArbitrumOne
    },
    new SupportedPayment
    {
        Asset = "USDT",
        Network = PaymentNetwork.BnbSmartChain
    }
};

Now validation becomes more useful:

bool isValid = supportedPayments.Any(x =>
    x.Asset.Equals(selectedAsset, StringComparison.OrdinalIgnoreCase) &&
    x.Network == selectedNetwork
);

If isValid is false, the application can stop the transaction and show a useful message to the user instead of attempting to process it.

Keep Supported Networks in Configuration

Hardcoding everything in the application can become inconvenient as the project grows.

A better approach for a real application is to keep supported networks in configuration.

For example:

{
  "SupportedNetworks": [
    "Polygon",
    "ArbitrumOne",
    "BnbSmartChain"
  ]
}

The application can then read this configuration when it starts.

This becomes particularly useful when the supported network list changes. You don't necessarily want to search through the codebase every time you need to update a payment configuration.

Validate Before Sending the Payment

The important part is when the validation happens.

The application should not wait until the actual blockchain transaction is being sent.

A simple flow could look like this:

User selects asset
        ↓
User selects network
        ↓
Validate asset + network
        ↓
Check wallet/payment details
        ↓
Process payment

If the network is unsupported, the flow should stop at the validation step.

This also gives the frontend an opportunity to show something meaningful, such as:

"This network is not currently supported. Please select another network."

That's much better than letting the user continue and discovering the problem after the transaction has already been initiated.

Why This Small Validation Matters

Blockchain transactions are different from many normal application requests because a mistake can be difficult to reverse.

A normal API request can often just be retried after fixing the input. With a blockchain transaction, sending an asset through the wrong network can create a much more serious problem.

That's why network validation shouldn't be treated as just a UI feature.

The frontend can prevent invalid selections, but the backend should validate them again before processing the payment. This way, even if someone bypasses the frontend or sends a modified request, the backend still has the final check.

Conclusion

Supporting multiple blockchain networks doesn't necessarily require complicated code. A good starting point is simply to keep the supported networks clearly defined and validate the asset + network combination before processing a payment.

As the application grows, the same idea can be extended with configuration files, database-driven payment settings, network-specific validation and proper transaction status handling.

The main thing is to validate early. In crypto payments, a small validation step can prevent a much bigger problem later.