Error: Uncaught (in promise): NullInjectorError: R3InjectorError(AppModule)[HttpClient -> HttpClient -> HttpClient]:
To resolve this problem HttpClient is Angular's mechanism for communicating with a remote server over HTTP.
To make HttpClient available everywhere in the app,
1- open the root AppModule,
2- import the HttpClientModule from @angular/common/http,
import { HttpClientModule } from '@angular/common/http';
3- add it to the @NgModule.imports array.
imports:[HttpClientModule, ]