Angular: @input boolean and ngIf not matching

(Sorry for my english, it's not my first language...)

I have some issue with some input paramaters I inject in my component when I call it with its template.

slider-multiple.component.ts :

import { Component, Input } from '@angular/core';

@Component({
  selector: 'slider-multiple',
  templateUrl: './slider-multiple.component.html'
 })
export class SliderMultipleComponent  {
   @Input() public modifiable: boolean;
 }

slider-multiple.component.html :

<button *ngIf="modifiable">Slider Button</button>

Call of the directive (for instance on app.component.html) :

<slider-multiple modifiable="activation"></slider-multiple>

With activation defined on app.component.ts :

export class AppComponent  {
   public activation : boolean = false ;

   public activate(){
     this.activation = !this.activation;
   }
 }

The button I defined on the html template of my component should be visible (through the *ngIf) only when the activation parameter of the directive is at true.

Does anyone knows why it don't work as expected ?

A Stackblitz to help .

Thanks in advance !