I do invoke data source on page but error "otnet: obj\Debug\netcoreapp3.0\Razor\Pages\AddCustomer.razor.g.cs(75,22): error CS1503: Argument 10: cannot convert from 'Microsoft.AspNetCore.Components.EventCallback' to 'Microsoft.AspNetCore.Components.EventCallback<QuanLyBanHang.Models.OtErp.TblSoCustomer>' [F:\GitHub02\RadZen-Projects\QuanLyBanHang\server\QuanLyBanHang.csproj]"
So the page is custom similar to auto-generated CRUD Add page? Can you check how the form is setup in your case? For CRUD Add page Radzen will generate Page load with new entity instance bound to the form like this: