In short, Web Scan Verification is required for web security scans, whereas Network Scan Verification is required for network security scans.
Web scan verification requires you to download a file which is unique to your scan target, and upload it to the root of the web site. Once the file has been uploaded to the root of your website, you can proceed with checking your website’s security.
Network scan verification requires that you confirm your account details, and request that we manually verify your details. Once your details are confirmed, you can proceed with checking your server’s security for network vulnerabilities.
More information can be found in the “Verifying Scan Target Ownership” section in the Configuring Targets documentation.