Inertia.js add vue plugin

Hi, im new to Laravel/ inertia.js and cant figure out how to add a vue plugin (ht tps://vuejsexamples.com/single-flash-message-with-vue/). My app.js looks like this:

require('./bootstrap');

import {createApp, h} from 'vue';
import {createInertiaApp} from '@inertiajs/inertia-vue3';
import {InertiaProgress} from '@inertiajs/progress';
import FlashMessage from '@smartweb/vue-flash-message';

const appName = window.document.getElementsByTagName('title')[0]?.innerText || 'Laravel';

const vueApp = createInertiaApp({
    title: (title) => `${title} - ${appName}`,
    resolve: (name) => require(`./Pages/${name}.vue`),
    setup({el, app, props, plugin}) {
        return createApp({render: () => h(app, props)})
            .use(plugin).use(FlashMessage)
            .mixin({methods: {route}})
            .mount(el);
    },
});

//vueApp.use(FlashMessage);


InertiaProgress.init({color: '#4B5563'});

Referencing it through

<FlashMessage></FlashMessage>

gives the following error:

TypeError: t is not a constructor

Any help is really appreciated.