Register a device for push notifications using expo-notifications and returning the Expo Push Token. Then send a push notification using the Expo Push Token.

registerForPushNotificationsAsync.js

import Constants from 'expo-constants';
import * as Notifications from 'expo-notifications';
import * as Permissions from 'expo-permissions';

const registerForPushNotificationsAsync = async () => {
  let token;
  if (Constants.isDevice) {
    const { status: existingStatus } = await Permissions.getAsync(
      Permissions.NOTIFICATIONS
    );
    let finalStatus = existingStatus;
    if (existingStatus !== 'granted') {
      const { status } = await Permissions.askAsync(Permissions.NOTIFICATIONS);
      finalStatus = status;
    }
    if (finalStatus !== 'granted') {
      alert('Failed to get push token for push notification!');
      return;
    }
    let res;
    try {
      res = await Notifications.getExpoPushTokenAsync();
      token = res.data;
    } catch (error) {
      alert(JSON.stringify(error));
    }
  } else {
    alert('Must use physical device for Push Notifications');
  }

  if (Platform.OS === 'android') {
    Notifications.setNotificationChannelAsync('default', {
      name: 'default',
      importance: Notifications.AndroidImportance.MAX,
      vibrationPattern: [0, 250, 250, 250],
      lightColor: '#FF231F7C'
    });
  }

  return token;
};

export { registerForPushNotificationsAsync };

sendPushNotification.js

const { Expo } = require('expo-server-sdk');

module.exports = async (expoTokens, message) => {
  const messages = [];
  expoTokens.forEach(expoToken => {
    messages.push({
      to: expoToken,
      sound: 'default',
      body: message,
      title: "Hello!"
    });
  });

  const expo = new Expo();
  const chunks = expo.chunkPushNotifications(messages);
  for (const chunk of chunks) {
    const ticketChunk = await expo.sendPushNotificationsAsync(chunk);
    console.log(ticketChunk);
  }
};