Blazor trigger custom validation message

I have the following class which is being used as an input model for an EditForm in a Blazor server side application.

public class KundeInput{    [ValidateComplexType]    public List<AnsprechpartnerInput> Ansprechpartner { get; } = new List<AnsprechpartnerInput>();    public string? Kundennummer { get; }    [Required]    [MaxLength(60)]    public string Firma { get; set; } = String.Empty;    [MaxLength(60)]    public string? Name2 { get; set; }    [MaxLength(60)]    public string? Name3 { get; set; }}

As you can see, my model contains a list of another model called AnsprechpartnerInput. Here is this model:

public class AnsprechpartnerInput{    public string? Kundennummer { get; set; }    public int Nummer { get; } = -1;    [MaxLength(60)]    [Required]    public string Vorname { get; set; } = String.Empty;    [MaxLength(60)]    [Required]    public string Nachname { get; set; } = String.Empty;    [MaxLength(40)]    [Required]    public string? Bereich { get; set; }    / * More properties */}

The validation works fine. However, once I have multiple invalid AnsprechpartnerInput models in my list, the ValidationSummary becomes a mess. Because it displays e.g. 5 times field xyz is invalid.

I know I can set a custom message with the ErrorMessage property but I am not able to use other attributes from my model in this message.

What I want to achive is this:

[Required(ErrorMessage = $"Vorname of {Kundennummer} is required")]public string Vorname { get; set; } = String.Empty;

I already tried to change the message with reflection but accoridng to Microsoft this way is not recommend or supportedhttps://github.com/dotnet/aspnetcore/issues/25611

Is there any way to get it to work? I thought of string replacement but I am not sure how I can figure out the right model for my ValidationMessage.

Also is there any way to validate the items of the list by one and get a boolean result? Let's say I want to achive this:

@foreach (var ansprechpartner in Input.Ansprechpartner){    if (Input.SelectedAnsprechpartner is null)        Input.SelectedAnsprechpartner = ansprechpartner;<a @onclick="() => Input.SelectedAnsprechpartner = ansprechpartner"       class="@GetNavListClass(Input.SelectedAnsprechpartner == ansprechpartner)"       id="list-ansprechpartner-tab-@(ansprechpartner.Nummer)"       data-toggle="list"       href="#list-ansprechpartner-@(ansprechpartner.Nummer)"       role="tab"       aria-controls="@(ansprechpartner.Nummer)">        @((MarkupString)(ansprechpartner.Nummer < 0  ? "<span class=\"font-weight-bold\">NEU</span>" : $"({ansprechpartner.Nummer})")) @ansprechpartner.Vorname @ansprechpartner.Nachname</a>    // When the model ansprechpartner is invalid, I want to display an icon}

Thanks for any help!PS: Blazor rocks!