You may experience this error when you try to set up the PayPal Express checkout gateway with API credentials directly from your PayPal account.
Following are the two major reasons for the error:
Using incorrect API credentials while configuring PayPal Express Checkout
Configuring Chargebee's test site with PayPal's live site credentials or vice versa
The above error indicates you are using incorrect API credentials. If you are convinced that credentials are correct check the endpoint. You can also contact Paypal support for more information on your Paypal API credentials.
Note: Sandbox credentials will not be valid in the production environment and live credentials will produce this error in the sandbox.
Kindly contact support if the issue persists. Here's our document on Paypal Express Checkout for your reference.
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