test.cs

public class CollabHub : Hub
{
    public async Task SetEditableRegionSync(EditableRegionSync editableRegionSync)
    {
        await Clients.All.SendAsync("ReceiveRegionSync", editableRegionSync);
    }
}

public class EditableRegionSync
{
    public string User { get; set; }
    public int RegionId { get; set; }
    public string Document { get; set; }
}