In your access token settings, you can choose to limit the domains that have access to your access token. Only do this if your API is integrated client-side, for example in the checkout of your eCommerce store.
1) Go to Access Tokens & Statistics in the account menu
2) Click on your access token. If you have more than one token, click on the one you want to edit.
3) On the configuration tab, scroll down to Allowed Domains. When this field is empty your token can be used on any web domain. As soon as you have added and saved domains to this box your token will only work for searches through those domains. Make sure you add all the required domains.