## TL;DR

Error map: 400 malformed or duplicate resource, 401 bad credentials, 403 no access or billing limit, 429 rate limit, 501 UNIMPLEMENTED means the method does not exist on that path (fix the route, never retry). SINCH_APP_ID is the Conversation API app identifier from the apps dashboard; SINCH_PROJECT_ID is the project/account identifier.

## Fix

1. Error map: 400 malformed or duplicate resource, 401 bad credentials, 403 no access or billing limit, 429 rate limit, 501 UNIMPLEMENTED means the method does not exist on that path (fix the route, never retry).
   Expected: You get the expected result; the problem is gone.

## When to use

- You are setting up or using this Sinch Conversation API feature.
- The symptom matches: region mismatch causes 404, and App ID is not Project ID.

## When NOT to use

- Unrelated Sinch Conversation API issues (different feature, different failure).
- You need general documentation for the tool; check the official docs instead.

## Compatibility

Reported against Sinch Conversation API. Source: https://github.com/sinch/sinch-plugins/blob/HEAD/plugins/sinch-claude-plugin/skills/conversation-api/SKILL.md.

## Variant phrasings

### region mismatch causes 404, and App ID is not Project ID

## Why it happens

The two most common Sinch integration failures are swapped identifiers and a wrong region base URL. Both produce confusing errors.

## Edge cases

- If your error message differs even slightly, this is probably a different issue; search the exact text.
- If the fix does not help, capture the full error output and check the source link for updates.

## Source

https://github.com/sinch/sinch-plugins/blob/HEAD/plugins/sinch-claude-plugin/skills/conversation-api/SKILL.md

---

## Vectle citations

- Exact version: <https://vectle.com/skills/skl_Z8BicjP4AoGGoJaPl3rX9Q/versions/skv_yKxQ7DcQuIKdqSuHN5FDTQ>
- Canonical HTML skill page: <https://vectle.com/skills/skl_Z8BicjP4AoGGoJaPl3rX9Q>
- Current Markdown URL: <https://vectle.com/skills/skl_Z8BicjP4AoGGoJaPl3rX9Q/markdown>

## Selected public attribution and original notices/references

```json
{
  "author": "issueatlas",
  "client": null,
  "notices_and_references": [
    "https://github.com/sinch/sinch-plugins/blob/HEAD/plugins/sinch-claude-plugin/skills/conversation-api/SKILL.md"
  ]
}
```