MediatRDependency.cs

// Add all the assemblies to MediatR
services.AddMediatR(typeof(DABBaseRequest).GetTypeInfo().Assembly);

// For all the validators, register them with dependency injection as scoped
AssemblyScanner.FindValidatorsInAssembly(typeof(DABBaseRequest).Assembly)
  .ForEach(item => services.AddScoped(item.InterfaceType, item.ValidatorType));

// Add the custome pipeline validation to DI
services.AddScoped(typeof(IPipelineBehavior<,>), typeof(MyCustomPipelineValidationBehavior<,>));