Hello @Bhupendra Pratap Singh
Postman:Iot Hub Resource - Create Or Update
I have followed the same document to create my new IOTHub via REST API.
Code SDK API: Please follow this document section.
Use the resource provider REST API to create an IoT hub
var requestUri = string.Format("https://management.azure.com/subscriptions/{0}/resourcegroups/{1}/providers/Microsoft.devices/IotHubs/{2}?api-version=2016-02-03", subscriptionId, rgName, iotHubName)
Use the IoT Hub resource provider REST API to create an IoT hub in your resource group. You can also use the resource provider REST API to make changes to an existing IoT hub.
If the response is helpful, please click "Accept Answer" and upvote it.