API token allows you to authenticate yourself while making email verification API calls. For security reasons, we suggest you keep changing this token occasionally to keep your account secure and also because its known to be a good practice in the industry.
Assuming you have logged into your account, click on "My Account" by either hovering over your name or display picture.
From the tabs displayed, choose "API & Integration" by clicking on it. You will see a screen much similar to this. Click on "Reset" button which will popup a warning window. Click "Ok" on the warning window and your API token should now be different to what you started off with.
Update your API token on all the applications using it. Failure to update the API token will result in authentication failure and thereby fail on any email verification calls your application or form might make.
(P.S. Don't even think about using our API token...Its already been reset)