When you create a new App Service Certificate you need to associate a Key Vault to the Certificate.
When doing this if you have no existing Key Vault you can click an "Add" button to create a new one within the certificate. This functionality no longer works and the deployment fails with an error and Microsoft Support suggested I add this here.
The workaround is to create the Key Vault normally, then go back to the Certificate.
If this feature isn't going to be fixed, I believe the "Add" button should be removed.
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