Within your installation settings you have the option to limit AddressComplete to accept requests only from specified IP addresses. This is a security feature that allows you to restrict who can use your AddressComplete service.
If you received an email that states, “This installation cannot be used from this IP address. The security settings may not include this IP address”, it means an attempt was made to use AddressComplete from another IP address. The IP address in question will be provided in the email.