tailwind-nextjs-blog/pages/api/convertkit.ts

import { NextApiRequest, NextApiResponse } from 'next';

/* eslint-disable import/no-anonymous-default-export */
export default async (req: NextApiRequest, res: NextApiResponse) => {
  const { email } = req.body;

  if (!email) {
    return res.status(400).json({ error: 'Email is required' });
  }

  try {
    const FORM_ID = process.env.CONVERTKIT_FORM_ID;
    const API_KEY = process.env.CONVERTKIT_API_KEY;
    const API_URL = process.env.CONVERTKIT_API_URL;

    // Send request to ConvertKit
    const data = { email, api_key: API_KEY };

    const response = await fetch(`${API_URL}forms/${FORM_ID}/subscribe`, {
      body: JSON.stringify(data),
      headers: {
        'Content-Type': 'application/json',
      },
      method: 'POST',
    });

    if (response.status >= 400) {
      return res.status(400).json({
        error: `There was an error subscribing to the list.`,
      });
    }

    return res.status(201).json({ error: '' });
  } catch (error) {
    return res.status(500).json({ error: error.message || error.toString() });
  }
};