What kind of security measures do you use?
All user access is protected by an Secure Access Token that is connected to your account profile, as well as your IP Address.
If the access token is submitted from an IP Address that is not recognized as connected to your account, the search will fail.
Your Access Token is assigned to the APIs you have subscribed to ensure access control. In certain cases, it may also apply to coverage areas such as States, County FIPS codes, or MLS Names.