What is the problem ASP.Net Core Error CS1061

Severity Code Description Project File Line Suppression State
Error CS1061 ‘IServiceCollection’ does not contain a definition for
‘AddDefaultIdentity’ and no accessible extension method
‘AddDefaultIdentity’ accepting a first argument of type
‘IServiceCollection’ could be found (are you missing a using directive
or an assembly
reference?) WebHesab C:UsersDELLsourcereposWebHesabWebHesabStartup.cs 36 Active