nodejs firebase function

function sendNotification(userId) {
  //get the userId of the person receiving the notification because we need to get their token
  const receiverId = userId;
  //get the token of the user receiving the message
  return admin
    .database()
    .ref(`/users/${receiverId}/settings`)
    .once("value")
    .then(snapshot => {
      const token = snapshot.child("msgToken").val();
      console.log("token: ", token);

      if (typeof token !== "undefined" && token !== null) {
        //we have everything we need
        //Build the message payload and send the message
        console.log("Construction the notification message.");
        const payload = {
          notification: {
            title: "Du har precis tjänat 150 tvätt-credits!",
            body:
              "Du har en kompis som har registrerat sig med din inbjudningskod, samt genomfört sitt första köp. Se status på dina credits i appen under ”Bjud in en vän”.",
            sound: "default",
            badge: "1"
          },
          data: {
            type: "invitation"
          }
        };
        return admin
          .messaging()
          .sendToDevice(token, payload)
          .then(function(response) {
            console.log("Successfully sent message:", response);
            console.log(response.results[0].error);
          })
          .catch(function(error) {
            console.log("Error sending message:", error);
          });
      }
    });
}