A 401 from the API means the request either didn't include a valid token, or the token isn't recognised. Four common causes:
1. Missing header
Every authenticated request needs Authorization: Bearer vs_xxx. Check your client actually sends it (curl -v is your friend).
2. Wrong prefix
The token must start with vs_. If you're passing something else (a raw key ID, a JWT header, etc.) you'll get 401.
3. Revoked token
Check Account Settings > API Keys. If the key you're using shows as revoked (or missing entirely), generate a new one.
4. Wrong environment
If you have keys for staging and production, make sure the one you're using matches the environment you're calling. Production keys don't work on staging and vice versa.