Here is how to buy credits for Keywords Everywhere
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
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.
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 buy credits. Clicking this link will take you to the pricing page where you can choose the package you want to buy.