Buttondown

import fetch from 'isomorphic-unfetch';

export default async (_, res) => {
  const API_KEY = process.env.BUTTONDOWN_API_KEY;
  const response = await fetch('https://api.buttondown.email/v1/subscribers', {
    headers: {
      Authorization: `Token ${API_KEY}`,
      'Content-Type': 'application/json'
    },
    method: 'GET'
  });

  const { count } = await response.json();

  return res.status(200).json({ count });
};

Usage

First, create a Buttondown account.

From the Settings page, retrieve your API key.

To securely access the API, we need to include the secret with each request. We also do not want to commit secrets to git. Thus, we should use an environment variable. Learn how to add environment variables in Vercel.