Hi @Matt Canfield ,
There are two common causes of the "Error: ajaxExtended call failed" error:
1.Most commonly this error occurs if permissions are missing. You might not have the permissions to perform the operation. Sometimes this can happen if you are using a custom RBAC group that doesn't have enough permissions to execute certain operations. If this is the case, you need to contact the administrator for your subscription and ensure that you have the rights granted to create the Key Vault (for example, Key Vault Administrator role).
2.This error can also occur if the resource provider is not registered under your subscription and needs to be registered. You can verify and register the resource providers under Subscriptions > your subscription > Settings > Resource providers. The Microsoft.KeyVault resource provider should be added automatically, but you can go to the settings and register anything that is missing. https://learn.microsoft.com/en-us/azure/azure-resource-manager/management/resource-providers-and-types
If neither of these root causes apply to your scenario, feel free to send me an email at AzCommunity@microsoft.com ("Attn: Marilee Turscak") and include your subscription ID and a link to this thread. If you are able to share more details about your scenario and screenshots from your portal, I can get a support case opened to address this issue and confirm if there might be a separate issue.
If the information helped you, please Accept the answer. This will help us as well as others in the community who may be researching similar questions.