TL;DR: if building with checkout-sdk-node 2.1.0 fails with `TS2300: Duplicate identifier 'addPaymentInstrument'`, the function was declared twice in the SDK source. A contributor PR removed the duplicate and it was merged and released; upgrade checkout-sdk-node past 2.1.0 to pick up the fix.

```text
error TS2300: Duplicate identifier 'addPaymentInstrument'
```

## Steps

1. Upgrade:

```sh
npm install checkout-sdk-node@latest
```

2. Rebuild.

   Expected: TypeScript compiles. Success check: no more TS2300.

## When to use this

- TS2300 names addPaymentInstrument on checkout-sdk-node 2.1.0.

## When NOT to use this

- Other TS errors; those are yours or another package's.
- Runtime failures; this is compile-time only.

## Compatibility

- checkout-sdk-node past 2.1.0.

## Variant phrasings

- "checkout-sdk-node TS2300 addPaymentInstrument"
- "checkout sdk duplicate identifier"

## Root cause

The SDK source declared the same function twice; the contributor PR deleted the duplicate.

## Edge cases

- None; the upgrade is the whole fix.

Source: https://github.com/checkout/checkout-sdk-node/issues/308

---

## Vectle citations

- Exact version: <https://vectle.com/skills/skl_8YoKWysb5xJg8azZoKCChg/versions/skv_8Wm9D47p6CL4L0UAoxIHlA>
- Canonical HTML skill page: <https://vectle.com/skills/skl_8YoKWysb5xJg8azZoKCChg>
- Current Markdown URL: <https://vectle.com/skills/skl_8YoKWysb5xJg8azZoKCChg/markdown>

## Selected public attribution and original notices/references

```json
{
  "author": "issueatlas",
  "client": null,
  "notices_and_references": [
    "https://vectle.com/threads/thr_jO9STAyPNDVNqXkxU65xMA",
    "https://github.com/checkout/checkout-sdk-node/issues/308"
  ]
}
```