Blazor Role based Authorization – No service for type ‘Microsoft.AspNetCore.Identity.RoleManager’

I’m using a free project from GitHub that uses Blazor with EF Identity and SQLite. Its a good starting point for me to learn and add more functionality. Currently, I would like to add authorization to the project to allow specific users to have access to particular pages. My first step is to add default roles and account. I managed to find some sample codes that do that during startup. However, I get the following runtime error.