RadzenDropDown Error and basic setup

I've looked at several posts, but I still can't seem to wrap my head around getting the DropDown to work correctly. Despite what I try, I keep getting this error:
crit: Microsoft.AspNetCore.Components.WebAssembly.Rendering.WebAssemblyRenderer[100] Unhandled exception rendering component: Specified cast is not valid. System.InvalidCastException: Specified cast is not valid. at Radzen.DropDownBase1.d__65[[System.Collections.Generic.List1[[System.String, System.Private.CoreLib, Version=5.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e]], System.Private.CoreLib, Version=5.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e]].MoveNext() at Radzen.Blazor.RadzenDropDown1.d__18[[System.Collections.Generic.List1[[System.String, System.Private.CoreLib, Version=5.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e]], System.Private.CoreLib, Version=5.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e]].MoveNext() at Microsoft.AspNetCore.Components.ComponentBase.CallStateHasChangedOnAsyncCompletion(Task task) at Microsoft.AspNetCore.Components.RenderTree.Renderer.GetErrorHandledTask(Task taskToHandle)

Here is the components code:
@page "/Test"

test



<RadzenDropDown AllowClear="true" AllowFiltering="true" FilterCaseSensitivity="FilterCaseSensitivity.CaseInsensitive"
@bind-Value=@Keywords Multiple="true" Placeholder="Select..." Data=@MasterKeywords
TextProperty="Keyword" ValueProperty="KeywordID" MaxSelectedLabels="4" Change="@(args => OnChange(args, "DropDown"))"
Style="width:650px" />
</div>
@code {

List<workingkeyworddef> MasterKeywords { get; set; } = new List<workingkeyworddef>();
List<string> Keywords { get; set; } = new List<string>();


protected async override Task OnInitializedAsync()
{
    MasterKeywords.Add(new workingkeyworddef { Keyword = "First test", KeywordID = "1" });
    MasterKeywords.Add(new workingkeyworddef { Keyword = "Second test", KeywordID = "2" });
    MasterKeywords.Add(new workingkeyworddef { Keyword = "Third test", KeywordID = "3" });

    Keywords.Add("2");
}

void OnChange(object args, string msg)
{
    var str = args is IEnumerable<object> ? string.Join(", ", (IEnumerable<object>)args) : args;
}

public class workingkeyworddef
{
    public string KeywordID { get; set; }
    public string Keyword { get; set; }
}
}