Thanks for reaching here! Looking at the error:
"Key Vault configuration missing for the App Service Certificate.
Could you please ensure that you've also carried out the following steps:
- Navigate to the Certificate Configuration section within the Certificate Properties page.
- Select "Step 1: Store" to store this certificate in Azure Key Vault.
- On the Key Vault Status page, you can choose either to use an existing Key Vault by clicking on "Key Vault Repository" or create a new Key Vault within the same subscription and resource group by selecting "Create New Key Vault."
- Once you've made your choice and selected the Key Vault Repository to store this certificate, the "Store" option should become visible.
You may refer to below these links-
- FAQ SSL certificates for Web Apps and App Service Certificates
- Internals of App Service Certificate -
- Domain verification is not working
Please let us know if issue remains.