You created an App Service plan named Plan1 and a web app webapp1, but the option to create a staging slot is not available. What should you do first to enable a staging slot for Plan1?

Staging slots, also known as deployment slots, are a feature of Azure App Service that allow you to deploy different versions of your web app to separate environments. This functionality is only available for App Service plans running on Standard, Premium, or Isolated tiers. The most common reason for not seeing the option to create a staging slot is that the App Service plan is currently running on a Basic or Free tier. Therefore, scaling up the App Service plan Plan1 to a supported tier (e.g., Standard or higher) is the first step to enable staging slots. Changing webapp1's Application settings, adding a custom domain, or scaling out the App Service plan (which increases instance count within the same tier) do not enable deployment slot functionality, as these actions do not change the underlying service tier that supports this feature.