Many merchants using Cloudflare send the Cloudflare IP to NoFraud instead of the end-user IP. It is critical to successful transaction screening that NoFraud obtains the end-user IP. In order to fix your settings to ensure that NoFraud receives the correct IP, please go into your DNS settings for Cloudflare and click the gray cloud (image below) to turn off your proxy:
When the cloud is gray, the proxy is turned off, and NoFraud is able to receive the end-user IP. An alternative option to this solution is to look into other CDN products supported by Shopify and available within the Shopify platform.
Please reach out to your account manager with any additional questions.