# How to bind a license to multiple identifiers, serially

QLM can bind a license to a computer identifier, such as a computer name, volume serial number, motherboard serial number, etc.

In some cases, depending on the manufacturer of a device, the device does not return a unique identifier as expected.

To circumvent these scenarios, you can create a fallback identifier, in case the first one does not return a value.

To implement such as scenario, you would need to do the following:

* Set the QlmLicenseBinding property to UserDefined.
* In your code, create an instance of QlmHardware and call the required method such as GetMotherBoardSerialNumber ().
* If the value returned by GetMotherBoardSerialNumber() is not empty, use it as input to any API that requires a computerID such as LicenseValidator.ValidateLicenseAtStartup
* If the value returned is empty, call your next preferred identifier, for example, QlmHardware.GetBiosUuid() or QlmHardware.GetMachineName()
* You can repeat this logic as often as needed.

When launching the QLM License Wizard, add the /computerID argument and pass the unique identifier that you computed.

Example:

{% code overflow="wrap" %}

```csharp
string GetUniqueIdentifier()
{
    QlmHardware hw = new QlmHardware();
    string computerID = hw.GetMotherBoardSerialNumber();
    if (String.IsNullOrEmpty(computerID))
    {
        computerID = hw.GetFirstVolumeSerialNumber ();
        if (String.IsNullOrEmpty(computerID))
        {
                computerID = hw.GetMachineName();
        }
    }
}
// Example when to call GetUniqueIdentifier
LicenseValidator lv = new LicenseValidator ();
lv.ValidateLicenseAtStartup (GetUniqueIdentifier(), ...);
 
// When launching the wizard
string args = String.Format ("/settings \"{0}\" /computerID {1}", settingsXmlFile, GetUniqueIdentifier());
lv.QlmLicenseObject.LaunchProcess ("QlmLicenseWizard.exe", args, true, true);
```

{% endcode %}


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