Firebase Functions Error on Deploy When Using MailerSend: MailerSend is not a constructor

Question

I am using MailerSend with Firebase Functions. Since Firebase Functions cannot be used with ES6 I am using V1 of MailerSend's NodeJS SDK. The SDK shows the following code for sending an email.

const Recipient = require("mailersend").Recipient;
const EmailParams = require("mailersend").EmailParams;
const MailerSend = require("mailersend");

const mailersend = new MailerSend({
    api_key: "key",
});

const recipients = [
  new Recipient("[email protected]", "Your Client")
];

const emailParams = new EmailParams()
      .setFrom("[email protected]")
      .setFromName("Your Name")
      .setRecipients(recipients)
      .setReplyTo("[email protected]")
      .setReplyToName("Reply to name")
      .setSubject("Subject")
      .setHtml("This is the HTML content")
      .setText("This is the text content");

mailersend.send(emailParams);

I am adding this code to index.js in my Firebase Functions Folder.

functions
    -index.js

When I deploy the code to Firebase Functions with the Firebase CLI command below I get an error stating.

Error: Functions codebase could not be analyzed successfully. It may have a syntax or runtime error

firebase deploy --only functions 

I ran the debug option on functions shown below and am getting the following.

Got response code 400; body Failed to generate manifest from function source: TypeError: MailerSend is not a constructor shutdown requested via /__/quitquitquit

firebase deploy --only functions --debug

I have not idea why this would be the case. For more clarity I removed as much code from the MailerSend sample above to recreate the error. I have added a simple index.js file where the error occurs and my package.json file.

index.js

const functions = require('firebase-functions')
require('dotenv').config()

const MailerSend = require('mailersend')

const MAILERSEND_API_KEY = process.env.MAILERSEND_API_KEY

const mailersend = new MailerSend({
    api_key: MAILERSEND_API_KEY,
})

package.json

{
    "name": "functions",
    "description": "Cloud Functions for Firebase",
    "scripts": {
        "lint": "eslint .",
        "serve": "firebase emulators:start --only functions",
        "shell": "firebase functions:shell",
        "start": "npm run shell",
        "deploy": "firebase deploy --only functions",
        "logs": "firebase functions:log"
    },
    "engines": {
        "node": "16"
    },
    "main": "index.js",
    "dependencies": {
        "@sentry/node": "^7.54.0",
        "axios": "^1.5.0",
        "dotenv": "^16.3.1",
        "firebase-admin": "^11.5.0",
        "firebase-functions": "^4.2.0",
        "mailersend": "^2.2.0",
        "stripe": "^13.7.0"
    },
    "devDependencies": {
        "@sentry/browser": "^7.54.0",
        "@sentry/tracing": "^7.54.0",
        "eslint": "^8.15.0",
        "eslint-config-google": "^0.14.0",
        "firebase-functions-test": "^3.0.0"
    },
    "private": true
}

Any help would be greatly appreciated.