How can I go back to the unchecked at Ionic 5?

<ion-item lines="none">
   <ion-label class="ion-text-wrap">{{'Order.Permission' | translate}}</ion-label>
   <ion-checkbox [(ngModel)]="isPermit" (ionChange)="permissionChange($event)"></ion-checkbox></ion-item>
permissionChange(ev) {
    if (ev.detail.checked) {
       this.myService.get().pipe(take(1)).subscribe(
       () => { 
          this.isPermit = true;
        },
        error => this.isPermit = false
      );
    }
  }

Even the isPermit set to false by the error return, the check box is still checked. I tried with the checked property, not ngModel. But there is no difference. I am on Ionic 5 and Angular 9.