Published module is broken: it's a CJS module instead of ESM

[jeremv42]

Environment

• Checkout SDK version: 3.1.0
• Platform and version: Node 24.13.1
• Operating System and version: MacOS 26.3 (25D125)

Description

Recently published SDK 3.1.0 is broken: it says that it's an ESM module but it's CJS, previous version (3.0.3) was fine.

Expected behavior

Correct ESM module

Current behavior

import { Checkout } from 'checkout-sdk-node';
         ^
SyntaxError: The requested module 'checkout-sdk-node' does not provide an export named 'Checkout'
    at #asyncInstantiate (node:internal/modules/esm/module_job:319:21)
    at async ModuleJob.run (node:internal/modules/esm/module_job:422:5)
    at async onImport.tracePromise.__proto__ (node:internal/modules/esm/loader:661:26)
    at async asyncRunEntryPointWithESMLoader (node:internal/modules/run_main:101:5)

Steps to reproduce

Import the SDK in a ESM module

Possible solution

• Revert publish commands to 3.0.3 (it was ok)
  or
• remove "type": "module" from package.json but I think that it's a regression

Additional information

[IamHamud]

Can confirm this issue. I hit the same ESM/CJS incompatibility while building [checkout-mcp-server] for learning purposes, on (https://github.com/IamHamud/checkout-mcp-server) — an MCP server that wraps 28 Checkout.com API endpoints.

The SDK declares "type": "module" in package.json but the published code uses CJS patterns (require, module.exports). This means:

• import { Checkout } from 'checkout-sdk-node' fails in ESM projects (as reported above)
• require('checkout-sdk-node') fails in CJS projects because Node sees "type": "module" and refuses to load it as CJS

Neither module system works cleanly out of the box.

Suggested fix — dual-package exports:

{
  "exports": {
    ".": {
      "import": "./src/index.mjs",
      "require": "./src/index.cjs"
    }
  }
}

Or alternatively, remove "type": "module" and keep shipping CJS (which worked fine in v3.0.3), with an ESM wrapper that re-exports for import users.

I ended up bypassing the SDK entirely and calling the Unified Payments API directly with fetch(), which is what the MCP server runs on.

[joaopedrodcf]

Node since 18 can run ESM with require without an issue so we shouldn't move a project to CJS that uses ESM only the problem with this was probably on the release, as far as I can see from the dist of the release

Before
https://npmx.dev/package-code/checkout-sdk-node/v/3.0.3/dist%2Findex.js

Now
https://npmx.dev/package-code/checkout-sdk-node/v/3.1.0/dist%2Findex.js

Basically as we can see in the 3.0.3 the code was ESM and on the 3.1.0 is CJS which is why it breaks because its CJS code with a type=module in package json

The change that broke the release was this one: #421 the change in babel was done because of the tests but it affected the production build as it converted to CJS and it was because of the preset --presets=@babel/preset-env

@armando-rodriguez-cko