Hello , Welcome to MS Q&A
Ok to resolve this please try below steps
- Clear Cache/Browser Issue: Sometimes, a browser issue can cause problems with validation. Try clearing your browser’s cache, or use an incognito window or a different browser to see if that resolves the issue.
- Use Azure CLI/PowerShell: If the portal keeps giving you this error, you can try creating the vault using the Azure CLI or PowerShell. This might bypass the issue with the portal.
Please try above two steps and let us know if any further questions or queries
Kindly accept answer if it helps
Thanks
Deepanshu