Hi,
Based on your description, you cannot add an alias anymore. Please note that Microsoft allows a maximum of 10 aliases to be added to your account within 12 months. This includes any aliases you have previously created and later removed.
Additionally, there is a short-term limit on adding an alias. You can only make up to two alias changes within 7 days. I recommend waiting 7 days before attempting to add your alias again.
If you require further assistance, please don't hesitate to let me know.
Stay Safe!