This error populates if you are using an incorrect set of REST API credentials, client ID and secret, for your specified environment, Sandbox vs. Live.
If you previously had your application set up for testing in the Sandbox environment, you may need to switch your current REST API credentials mode from Sandbox to Live (or vice versa).
Here's how:
- Log in to your PayPal Developer account.
- Click Dashboard.
- Select the app you'll be editing under Apps & Credentials.
- Toggle the app from Sandbox to Live or from Live to Sandbox.
- Use the Live or Sandbox API credentials displayed to set your credentials in your API call appropriately.
When you copy and paste your credentials into your application, ensure you do not copy any leading or trailing space as this may add an extra character space to your credentials that will populate this error.