Unable to Insert Data from Angular frontend to Laravel API whitch Model Relationship One to Many

I have Angular App connected with Laravel API. In Laravel API there are one to many relationship between Employee and Salary Models. when I try to insert data Only insert Employee Model data but not insert salary model data Employee Insert Controller is

public function addEmployee(Request $request) {
        $employee = Employee::create($request->all());
        $salary = $employee->salaries()->create($request->all());
        return response($employee, 201);
}

api route for insert

/add new Employee
Route::post('addEmployee','App\Http\Controllers\EmployeeController@addEmployee');

employee-add.html

<div class="detail-list">
    <h3>Employee Profile</h3>
    </div>
    <form (ngSubmit)="insertData()">
        <h4>Profile Detail</h4>
        
     <div class="form-group row">
        <label for="first_name" class="col-sm-2 col-form-label">First Name</label>
        <div class="col-sm-10">
        <input type="text" name="first_name" class="form-control" [(ngModel)]="employee.first_name">
        </div>
     </div>
     <br>
     <div class="form-group row">
        <label for="last_name" class="col-sm-2 col-form-label">Last Name</label>
        <div class="col-sm-10">
        <input type="text" name="last_name" class="form-control" [(ngModel)]="employee.last_name">
        </div>
     </div>
     <br>
     <div class="form-group row">
        <label for="birth_date" class="col-sm-2 col-form-label">Date of Birth</label>
        <div class="col-sm-10">
        <input type="date" name="birth_date" class="form-control" [(ngModel)]="employee.birth_date">
        </div>
     </div>
     <br>
     <div class="form-group row">
        <label for="hire_date" class="col-sm-2 col-form-label">Hire Date</label>
        <div class="col-sm-10">
        <input type="date" name="hire_date" class="form-control" [(ngModel)]="employee.hire_date">
        </div>
     </div>
     <br>
     <div class="form-group row">
        <label for="gender" class="col-sm-2 col-form-label">Gender</label>
        <div class="col-sm-10">
        <input type="text" name="gender" class="form-control" [(ngModel)]="employee.gender">
        </div>
     </div>
     <br>
     
     <h4>Salary Details</h4>
     
     <div class="salary-details"  >
       <div class="table">
          <div class="form-group row">
             <label for="salary" class="col-sm-2 col-form-label">Salary</label>
             <div class="col-sm-10">
             <input type="text" name="salary" class="form-control" [(ngModel)]="salary.salary">
             </div>
          </div>
          <br>
          <div class="form-group row">
             <label for="from_date" class="col-sm-2 col-form-label">From Date</label>
             <div class="col-sm-10">
             <input type="date" name="from_date" class="form-control" [(ngModel)]="salary.from_date">
             </div>
          </div>
          <br>
          <div class="form-group row">
             <label for="to_date" class="col-sm-2 col-form-label">To Date</label>
             <div class="col-sm-10">
             <input type="date" name="to_date" class="form-control" [(ngModel)]="salary.to_date">
             </div>
          </div>
          <br>
       </div>
     </div>
    
      
    <br>
    <button  class="btn btn-dark btn-sm mt-4 btnPosition">Add Employee</button>
    <br><br>
    </form>
    

angular data.service.ts for insert data

insertData(data: Employee) {
    return this.httpClient.post('http://127.0.0.1:8000/api/addEmployee', data);
  }

and employee-add.component.ts

export class EmployeeAddComponent implements OnInit {
  
  employees:any;
  employee = new Employee();
  salary: any;
  title: any;
  

  constructor(private dataService:DataService) {}
  ngOnInit(): void {
    
  }

  

  insertData() {
    this.dataService.insertData(this.employee).subscribe(res => {
      console.log(res);
      
    })
    
  }

}

Employee model like

export class Employee {
    birth_date:any;
    first_name:any;
    last_name:any;
    gender:any;
    hire_date:any;
salaries: any;
salary:any;
emp_no: any;
}

but console encontered following error msg about salary ERROR TypeError: ctx.salary is undefined I think I need relationship between Employee Model and Salary Model in Angular? how could I fix this matter