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Firstly, please make sure that you are using the correct Azure documentation for your API Management instance. The service tag "ApiManagement" is only available for API Management instances that are deployed in a virtual network. If your API Management instance is not deployed in a virtual network, then the "ApiManagement" service tag will not be available.
If your API Management instance is deployed in a virtual network, then please make sure that you have the correct permissions to view and use the service tags. You need to have the "Microsoft.Network/serviceTags/read" permission to view the list of available service tags. You can check your permissions by going to the Access control (IAM) tab in the Azure portal and selecting your subscription or resource group.
If you have the correct permissions and your API Management instance is deployed in a virtual network, but you still cannot find the "ApiManagement" service tag, then please try refreshing the list of available service tags by clicking on the "Refresh" button in the Azure portal. If the issue persists, please let me know and we can investigate further.
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