Error - export 'ɵɵdefineInjectable' was not found in '@angular/core' Root Cause - when we inject the service at both places in service @Inectable({providedin:root}) and in module provider also , then we face this error. @Injectable({ providedIn: 'root' }) export class NgxAuthService extends UserAgentApplication {} and in module we are registering service in provider as below. providers: [ { provide: MSAL_CONFIG, useValue: config }, NgxAuthService, { provide: WindowWrapper, useValue: window } ] Solution - replace above service class code as below. @Injectable() export class NgxAuthService extends UserAgentApplication {