Client Authentication failed error on Pay with Paypal click

Purchased Paypal module
Installed it
Inserted client email, id, and secret in Paypal module setup

But it fails during the checkout process, saying
Client Authentication failed

What should I fix?

tim

Did you follow the readme instructions how to get your API keys from Paypal?

#  Generate REST API credentials  #
###################################

To generate REST API credentials for the sandbox and live environments:

Log into the Developer Dashboard with your PayPal account credentials. If you don't have an account, you can click on the sign up option.

    https://developer.paypal.com/

On My Apps & Credentials, use the toggle to switch between live and sandbox testing apps.

Note: If you are creating a Sandbox app, you will also need to select a test business account that will act as the API caller. For more details, see Get Started.

Navigate to the REST API apps section and click Create App.

Type a name for your app and click Create App. The app details page opens and displays your credentials.

Copy and save the client ID and secret for your app.

Review your app details and save your app.
View code on GitHub