Not able to click nb-checkbox of Nebular theme angular

I am new to Nebular theme. I have a checkbox but it's not working.

HTML

<nb-checkbox [value]="checked" (change)="toggle($event)"></nb-checkbox>

TypeScript

  toggle(checked: any) {    
    this.checked = checked.target.checked;
  }

Module.ts

//import
import { NbCheckboxModule } from '@nebular/theme';

imports: [NbCheckboxModule]

toggle function is being called fine but checkbox is not being checked.

I have been debugging since a long time but couldn't identify the issue. Any suggestions about what could be wrong? Thank you.