How do I get an error message?

Hello to everyone,
I’m using Ionic 3 form validation. Everything works, but I want to display an error message if the required field is empty. Is there a way to do this?
Thanks in advance.

Example TS code:

import { Validators, FormBuilder, FormGroup } from ‘@angular/forms’;

private todo : FormGroup;

constructor(private view: ViewController,private formBuilder: FormBuilder, private auth: AuthServiceProvider) {
this.todo ={
name: [’’, Validators.required],
surname: [’’]

Html file code:

    <form [formGroup]="todo" (ngSubmit)="postData()"><ion-item>
            Müşteri Adı
        <ion-input type="text" formControlName="name" [(ngModel)]="" name="name" placeholder=""></ion-input>

            Müşteri Soyadı
        <ion-input type="text" formControlName="surname" [(ngModel)]="todo.surname" name="surname" placeholder=""></ion-input>
    <div class="spacer" style="height:30px;"></div>
    <button type="submit" [disabled]="!todo.valid" ion-button block>


Just put a span below your Input field like this:
<span *ngIf=„!your_input_field.isValid“>errormessage