A network device logs transmission control protocol (TCP) flow data for connections between registered devices that are registered for use of secure Internet of Things (IoT) application programming interfaces (APIs). The logging generates logged flow data. The network device receives, from a first registered device, a call validation request for an IoT API call directed to the first registered device from a second registered device. The call validation request includes packet information of the IoT API call. The network device compares the packet information with the logged TCP flow data. When the comparing indicates a match of the packet information and the logged TCP flow data, the network device sends a response to the first registered device to accept the IoT API call. Otherwise, the network device sends a response to the first registered device to reject the IoT API call.