Here is how to purchase a Keywords Everywhere subscription

1
Install the Chrome extension or Firefox add-on
Before you can buy credits, you need to have installed the Keywords Everywhere Chrome extension or Firefox add-on

2
Setup the API Key
Once the extension/add-on has been installed, you need to sign up for an API key and set it up.

3
Click the "K" icon at the top right of your browser
In the popup that opens, at the bottom, you will find the link to purchase a subscription. Clicking this link will take you to the pricing page where you can choose the plan you want to buy.