Making calls to the HIBP email address search API requires a rate limited key you can purchase on either a monthly or yearly basis. If you've already purchased a key, you'll be able to manage it after verifying you have access to the email address you wish to use (you'll receive a unique link to that address). If you need help, check out the FAQs and troubleshooting guide or submit a support request.
A rate limited key allowing 10 requests per minute
A rate limited key allowing 50 requests per minute
A rate limited key allowing 100 requests per minute
A rate limited key allowing 500 requests per minute