Trying to add AutoMapper to Asp.net Core 2?

You likely updated your ASP.NET Core dependencies, but still using outdated AutoMapper.Extensions.Microsoft.DependencyInjection package.

For ASP.NET Core you need at least Version 3.0.1 from https://www.nuget.org/packages/AutoMapper.Extensions.Microsoft.DependencyInjection/3.0.1

Which references AutoMapper 6.1.1 or higher.

AutoMapper (>= 6.1.1)

Microsoft.Extensions.DependencyInjection.Abstractions (>= 2.0.0)

Microsoft.Extensions.DependencyModel (>= 2.0.0)

The older packages depend on Microsoft.Extensions.DependencyInjection.Abstractions 1.1.0 and can't be used with ASP.NET Core since there have been breaking changes between Microsoft.Extensions.DependencyInjection.Abstractions 1.1.0 and 2.0

If you are using AspNet Core 2.2 and AutoMapper.Extensions.Microsoft.DependencyInjection v6.1 You need to use in Startup file

services.AddAutoMapper(typeof(Startup));