I'm receiving a function overload error when making component for API service

Question

I am trying to design an API with a backend server that receives calls from client side. I'm very new at using Typescript (I come from a Java background.) I get an error stating "No overload matches this call."

I created the basis for the services that will be called in this file:

//create functions that can reach backend by making http requests using httpclient

import { Injectable } from '@angular/core';
import {HttpClient} from '@angular/common/http';
import { Observable } from 'rxjs';
import { Employee } from './employee';
import { environment } from 'src/environments/environment';
//makes angular aware that this is your service
@Injectable({providedIn: 'root'})
export class EmployeeService {
//access to backend url connected to environments.ts
  private apiServerUrl = environment.apiBaseUrl; 
  //this allows requests to backend
  constructor(private http: HttpClient) {}
//gets list of all employees
//tells http client where to make the requests and type of requests
  public getEmployee(): Observable<Employee> {
    //common js technique to put variables and strings at same time
    return this.http.get<any>(`${this.apiServerUrl}/employee/all` ) //<-- get requrest
    }
  public addEmployee(employee: Employee): Observable<Employee> {
    //common js technique to put variables and strings at same time
    return this.http.post<Employee>(`${this.apiServerUrl}/employee/add`, employee); //<-- post request needed for adding
    }
    public updateEmployee(employee: Employee): Observable<Employee> {
      //common js technique to put variables and strings at same time
      return this.http.put<Employee>(`${this.apiServerUrl}/employee/add`, employee); //<-- post request needed for adding
      }
      //deleting empl will not send any response back, and thus use observable<void>
    public deleteEmployee(employeeId: number): Observable<void> {
      //common js technique to put variables and strings at same time
      return this.http.delete<void>(`${this.apiServerUrl}/employee/delete/${employeeId}`); //<-- post request needed for adding
    }
  }

this is the app.component.ts file

import { HttpErrorResponse } from '@angular/common/http';
import { Component, OnInit } from '@angular/core';
import { Employee } from './employee';
import { EmployeeService } from './employee.service';

@Component({
  selector: 'app-root',
  templateUrl: './app.component.html',
  styleUrls: ['./app.component.css']
})
export class AppComponent implements OnInit {
  public employees: Employee[];

  constructor(private employeeService: EmployeeService){}

  ngOnInit(){
    this.getEmployee();
  }
  public getEmployee(): void{
    //subscribed used so we are notified when data comes back from server
    this.employeeService.getEmployee().subscribe(
      (response: Employee[]) => {
        this.employees = response;
   },
    (error: HttpErrorResponse) => {
      alert(error.message);
    }
    );
  }
}