An Azure service that enables bidirectional communication between internet of things (IoT) devices and applications.
@Rani H Welcome to Q&A forum!
You haven't mentioned which SDK you are using and what documentation you have followed for the steps.
Please share the complete details/steps which led to this error message.
Incase if you haven't checked earlier, please refer Send messages from the cloud to your device with IoT Hub (.NET) and let us know if it helps.