Normally, I use onWillDestroy to cleanup the data before leaving the app. I added some notification to the POS but the callbackFn keeps getting called after I left the POS so I want to unsubscribe before I leave.

// original class in Point_of_Sale
export class PosStore extends Reactive {
	​async setup( .... )
}

// my modification
import { onWillDestroy } from "@odoo/owl";

patch(PosStore.prototype, {
  async setup() {
    await super.setup(...arguments);
    this.bus.addChannel("promoModule");
	​
	​let callbackFn = (data) => {....};

	this.bus.subscribe("REDALERT", callbackFn);
​
	​// doesn't work
	​onWillDestroy(async () => {
      this.bus.unsubscribe("REDALERT", callbackFn);
      this.bus.deleteChannel("promoModule");
	​});
  }
}

But this time it throws this owl error even I already use it in the setup function. It works fine if I remove the onWillDestroy.

OwlError: No active component (a hook function should only be called in 'setup')
    Error: No active component (a hook function should only be called in 'setup')
        at getCurrent (point_of_sale.assets_prod.min.js:1047:46)
        at onWillDestroy (point_of_sale.assets_prod.min.js:1108:39)
        at Proxy.setup (point_of_sale.assets_prod.min.js:15949:365)
        at async Proxy.setup (point_of_sale.assets_prod.min.js:15997:415)
        at async Promise.all (:8069/pos/index 0)
        at async start (point_of_sale.assets_prod.min.js:5219:1)
        at async _startServices (point_of_sale.assets_prod.min.js:5220:72)
        at async startServices (point_of_sale.assets_prod.min.js:5213:157)
        at async mountComponent (point_of_sale.assets_prod.min.js:5226:170)
        at async startPosApp (point_of_sale.assets_prod.min.js:15955:1188)

I'm not sure what cause the error. Is there something else I should try?