E-mail form handling returns Internal Server Error (500) on POST request (Next.js, Resend API)

Question

I came across the following error while trying to implement the form functionality. The code for my route is as follows:

//import { EmailTemplate } from "../../../components/EmailTemplate";
import { NextResponse } from "next/server";
import { Resend } from "resend";

const resend = new Resend(process.env.RESEND_API_KEY);
const fromEmail = process.env.FROM_EMAIL;

export async function POST(req, res) {
  const { email, subject, message } = await req.json();
  console.log("EMAIL DATA", email, subject, message);
  try {
    const data = await resend.emails.send({
      from: fromEmail,
      to: [fromEmail, email],
      subject: subject,
      react: (
        <>
          <h1>{subject}</h1>
          <p>Thank you for contacting me!</p>
          <p>New message submitted:</p>
          <p>{message}</p>
        </>
      ),
    });
    return NextResponse.json(data);
  } catch (error) {
    return NextResponse.json({ error });
  }
}

The code above is handled in the EmailSection JSX component, an excerpt is as follows:

const EmailSection = () => {
  const [emailSubmitted, setEmailSubmitted] = useState(false);

  const handleSubmit = async (e) => {
    e.preventDefault();
    const data = {
      email: e.target.email.value,
      subject: e.target.subject.value,
      message: e.target.message.value,
    };
    const JSONdata = JSON.stringify(data);
    const endpoint = "/api/send";

    const options = {
      method: "POST",
      headers: {
        "Content-Type": "application/json",
      },
      body: JSONdata,
    };

    const response = await fetch(endpoint, options);
    const resData = await response.json();

    if (response.status === 200) {
      console.log("Message sent.");
      setEmailSubmitted(true);
    }
  };

However, I get the internal server error while making a POST request:

POST http://localhost:3000/api/send

- error SyntaxError: Unexpected end of JSON input
    at JSON.parse (<anonymous>)
    at parseJSONFromBytes (node:internal/deps/undici/undici:6662:19)
    at successSteps (node:internal/deps/undici/undici:6636:27)
    at node:internal/deps/undici/undici:1236:60
    at node:internal/process/task_queues:140:7
    at AsyncResource.runInAsyncScope (node:async_hooks:203:9)
    at AsyncResource.runMicrotask (node:internal/process/task_queues:137:8)
    at process.processTicksAndRejections (node:internal/process/task_queues:95:5)

What could be an issue here? The code seems to be correct, so I leaning towards another explanation, for example some environment settings that I'm not aware of.