Go to your Stripe Account: 

Developers > API keys

Your account API Key is the one called: Secret Key. It is usually hidden and you need to reveal it in order to copy it. 

IMPORTANT: Be sure that your account should be in Live mode. API Key for test data is different and this will not work for production sites. It is very critical that you copy and paste the exact API Key with no additional characters.

On Stripe you will see this:

Go to Monetization > Products > Payment Gateways, the section on the Nunchee Console:

The STRIPE API KEY, is the SECRET KEY

The STRIPE PUBLIC KEY is the PUBLISHABLE KEY

Save it and go to the menu App Builder > Store Presence > Publish my App button > Select just the Web version (do not select IOS either Android) > Publish

Wait for 10 minutes so you can create your products on the menu Monetization > Products

Once you finish. You are already done!