Util function to send mails from cloud function

sendmailGun.js

const Mailgun = require('mailgun-js');

const DOMAIN = 'mail.myfortvest.com';
const API_KEY = process.env.MAIL_API_KEY || '';
const PUBLIC_KEY = process.env.MAIL_PUBLIC_KEY || '';
const mailgun = Mailgun({ apiKey: API_KEY, domain: DOMAIN, publicApiKey: PUBLIC_KEY });

const sendMail = async (payload) => {
   const {variable, desc, ...rest} = payload;
    const variableKey = Object.keys(payload.variable);
    const variableValues = Object.values(payload.variable);
    const message = {...rest};
    message.from = `${desc} <[email protected]>`;
    variableKey.forEach((key, idx) => {
        message[`v:${key}`] = variableValues[idx];
    });
    try {
        await mailgun.messages().send(message);
    } catch (error) {
        throw new Error(error);
    }
}

/**
 * Responds to any HTTP request.
 *
 * @param {!express:Request} req HTTP request context.
 * @param {!express:Response} res HTTP response context.
 */
exports.mailHandler = async (req, res) => {
  const payload = req.body.payload;
  return await Promise.all(payload.map((message) => sendMail(message)))
    .then(() => res.status(200).json({success: true}))
};

const testPayload = {
    "payload": [
        {
            "desc": "Accepted",
			"subject": "Request accepted",
			"template": "on-investee-accept",
			"to": "[email protected]",
			"variable": {
				"user": "Kelechi Oliver",
				"paymentLink": "https://myfortvest.com/pay/investee?u=jjsuudbbe"
			}
        }
    ]
}