Blazor 8 Edit Form can´t find Model or EditContext

In Blazor 8 I have a component with an Edit Form.

Whenever I submit the Form, I always get the following error:

InvalidOperationException: EditForm requires either a Model parameter, or an EditContext parameter, please provide one of these.

This is how the component looks (uses SSR Server Mode):

<Sheet cssClass="mb-3"><SheetTitle Text="Admin Area"></SheetTitle>    @if (Mini.Blocked)    {<div>This Miniature has been blocked by an Admin</div>    }    else    {<EditForm Model="@formData" FormName="BlockMiniature" method="post" OnSubmit="@OnBlockSubmit"><input type="hidden" value="@Mini.Id" name="formData.MiniatureId"/><TextareaField Name="formData.Reason" @bind-Value="formData.Reason"></TextareaField><div class="flex justify-center"><Button type="submit">Block Miniature</Button></div></EditForm>    }</Sheet>@code {    [Parameter]    public Miniature Mini { get; set; }    [SupplyParameterFromForm]    public BlockMiniatureForm formData { get; set; } = new();    public class BlockMiniatureForm    {        public Guid MiniatureId { get; set; }        public string Reason { get; set; }    }    public async Task OnBlockSubmit(EditContext arg)    {        BlockMiniatureForm form = (BlockMiniatureForm) arg.Model;        await mediatr.Send(new BlockMiniatureCommand(form.MiniatureId, form.Reason));    }}

I tried to add the Parameters to the Form with @ and without. Makes no difference :(