Nodemailer not sending mails with multiple attachments (Vercel Dev)

I have a react app and Vercel api connected with Stripe. I have set up a webhook where after a successful payment the email should be sent to my gmail with all the information about the order as well as images of the items. It all works very well if I attach up to 2 images. If there are more than 2 images attached the email does not get sent and no error messages are returned.

The webhook code

import { buffer } from "micro";
import Stripe from "stripe";
import type { VercelRequest, VercelResponse } from "@vercel/node";
import { storage } from "../src/utils/firebase.js";
import { ref, getDownloadURL } from "firebase/storage";
import bucket from "../src/utils/firebaseAdmin.js";

export default async function handler(req: VercelRequest, res: VercelResponse) {
  if (req.method === "POST") {
    let event: { [key: string]: any };
    const stripe = new Stripe(      "sk_test...........",
      { apiVersion: "2022-11-15" }
    );
    try {
      const requestBuffer = await buffer(req);
      const signature = req.headers["stripe-signature"] as string;

      event = stripe.webhooks.constructEvent(
        requestBuffer.toString(),
        signature,
        "whsec_................" 
      );
    } catch (error) {
      res.status(400).send(`Webhook error: ${error}`);
      return;
    }

    //remove images from firebase
    const deleteImageFromFirebase = async (user: string) => {
      await bucket.deleteFiles({ prefix: `temp/${user}` });
    };

    const user = event.data.object.metadata.user;

    switch (event.type) {
      case "checkout.session.completed": {
        const sessionWithLineItems = await stripe.checkout.sessions.retrieve(
          event.data.object.id,
          {
            expand: ["line_items"],
          }
        );
        const lineItems = sessionWithLineItems.line_items;
        const purchasedItems = lineItems?.data.map(
          (item: { [key: string]: any }) => {
            return item.description;
          }
        );

        //send email to own email about new order
        let imgUrls: { [key: string]: any }[] = [];
        for (let i = 0; (purchasedItems as string[]).length > i; i++) {
          const myRef = ref(storage, `temp/${user}/${i}.png`);
          const downloadUrl = await getDownloadURL(myRef);
          imgUrls.push({ filename: `${i + 1}.png`, path: downloadUrl });
        }
        const email = event.data.object.customer_details.email;
        const name = event.data.object.customer_details.name;
        const to = "[email protected]";
        const from = `New order from ${name} <.....@....>`;
        const subject = `There is a new order from ${name}`;

        try {
          await fetch("http://localhost:3001/api/submitForm", {
            method: "POST",
            headers: {
              "Content-Type": "application/json;charset=utf-8",
            },
            body: JSON.stringify({
              name: `${name}`,
              email: `${email}`,
              message: `There is a new order:
            ${purchasedItems?.map((item: string, i: number) => {
              return ` ${i + 1}: ${item}`;
            })}
           `,
              attachments: imgUrls,
              to: to,
              from: from,
              subject: subject,
              date: date,
              toCustomer: false,
            }),
          }).then(() => {
            //remove temporary images from firebase
            deleteImageFromFirebase(user);
          });
        } catch (e) {
          console.log(e)
          res.status(500).send(`Webhook error: ${e}`);
        }
        res.status(200);
        break;
      }
      case "checkout.session.expired": {
        //remove temporary images from database
        deleteImageFromFirebase(user);
        break;
      }
    }
  }
}

Nodemailer code

import type { VercelRequest, VercelResponse } from '@vercel/node';
import nodemailer from "nodemailer";

const allowCors =
  (fn: any) => async (req: VercelRequest, res: VercelResponse) => {
    res.setHeader("Access-Control-Allow-Credentials", "true");
    res.setHeader("Access-Control-Allow-Origin", "*");
    res.setHeader(
      "Access-Control-Allow-Methods",
      "GET,OPTIONS,PATCH,DELETE,POST,PUT"
    );
    res.setHeader(
      "Access-Control-Allow-Headers",
      "X-CSRF-Token, X-Requested-With, Accept, Accept-Version, Content-Length, Content-MD5, Content-Type, Date, X-Api-Version"
    );
    if (req.method === "OPTIONS") {
      res.status(200).end();
      return;
    }
    return await fn(req, res);
  };

async function submitForm(req: VercelRequest, res: VercelResponse) {
  if (req.method === "POST") {
    const name = req.body.name;
    const email = req.body.email;
    const message = req.body.message;
    const to = req.body.to;
    const from = req.body.from;
    const subject = req.body.subject;
    const attachments = req.body.attachments || [];
    const toCustomer = req.body.toCustomer;

    const contactEmail = nodemailer.createTransport({
      host: "smtp.gmail.com",
      port: 465,
      secure: true,
      auth: {
        user: process.env.EMAIL_USER,
        pass: process.env.EMAIL_PASS,
      },
    });

    await new Promise((resolve, reject) => {
      contactEmail.verify((error, success) => {
        if (error) {
          console.log(error);
          reject(error);
          res.status(500).send(`Nodemailer error: ${error}`);
        } else {
          console.log("Ready to Send");
          resolve(success);
        }
      });
    });

    const mailInfo = {
      from: from,
      to: to,
      subject: subject,
      html: toCustomer
        ? `<p>${message}</p>`
        : `<p>Nombre: ${name}</p>
             <p>Correo: ${email}</p>
             <p>Mensaje: ${message}</p>`,
      attachments: attachments,
    };

    await new Promise((resolve, reject) => {
      console.log("inside promise before send")
      contactEmail.sendMail(mailInfo, (error, info) => {
        console.log("inside send");
        if (error) {
          console.log(error)
          reject(error);
          res.status(500).send(`Nodemailer error: ${error}`);
        } else {
          console.log(info)
          resolve(info);
          res.status(200);
        }
      });
    });
    console.log("end")
  }
}

export default allowCors(submitForm);

logs when I am attaching 1 image (850kb - 2.5mb)

Ready to Send
inside promise before send
inside send
{
 ...info
}
end

logs when I am attaching 4 images or more (~800b/img)

Ready to Send
inside promise before send

logs of attachments

[ { filename: '1.png', path: 'firebasestorage.googleapis.com...' }, { filename: '2.png', path: 'firebasestorage.googleapis.com...' }, { filename: '3.png', path: 'firebasestorage.googleapis.com...' }, { filename: '4.png', path: 'firebasestorage.googleapis.com...' } ]

It never reaches "inside send" I was looking through everywhere and tried changing the code without any luck. Any ideas of what can be wrong or could fix it would be appreciated.