AAD application registration fail : The host name should not be based on already owned domain

Hi Experts:

I want to implement SSO in Excel Addin. I read this article https://docs.microsoft.com/en-us/office/dev/add-ins/develop/create-sso-office-add-ins-aspnet  and follow the step to register an application in https://apps.dev.microsoft.com . However I got a error message while I specify the application ID URI like below.

This domain name “xizhang.com” is owned by me, and I hosted this api site in azure, and set a custom domain name to it now. I don’t understand how to correct this problem.If you can give me some advice, that will be great. Thank you!