# VerifyPreviousVersionLicenseDelegate delegate

Namespace: [Rhino.PlugIns](https://developer.rhino3d.com/api/rhinocommon/namespace/rhino.plugins.md) · Assembly: [RhinoCommon](https://developer.rhino3d.com/api/rhinocommon/assembly/rhinocommon.md)

```cs
public delegate VerifyPreviousVersionLicenseDelegate
```

Called by GetLicense/AskUserForLicense to verify that a previous version license.

**Signature:**

```cs
bool VerifyPreviousVersionLicenseDelegate(string license, string previousVersionLicense, out string errorMessage)
```

**Parameters:**

- `license` ([string](https://learn.microsoft.com/dotnet/api/system.string)): License being entered in GetLicense
- `previousVersionLicense` ([string](https://learn.microsoft.com/dotnet/api/system.string)): Previous version license entered to verify upgrade eligibility
- `errorMessage` (out [string](https://learn.microsoft.com/dotnet/api/system.string)): Output parameter with localized error message to display to user when VerifyPreviousVersionLicenseDelegate returns false