When I am creating Alert from Azure Monitor services I found below massage restricted me to complete the process of creating alert after few search on Microsoft document I found that I need to register for the Microsoft.insights provider to my subscription and they we can do it from azure portal or using PowerShell.
Fix the issue using PowerShell command
Register-AzureRmResourceProvider –ProviderNamespace Microsoft.Insights
Fix the issue from Azure Portal
Under subscription in the left side select Resource provider and search about Microsoft.insights then do register for it easily