Ben Yang-楊家維, Apologies for the delayed response here.
Could you please try again to configure your host/domain and let us know .
In general, it is recommended to wait at least 24 hours after releasing a custom domain name or hostname before attempting to reuse it, to allow enough time for the DNS changes to propagate fully. However, in some cases, the domain name or hostname may become available for reuse sooner than that.
FAQ App Service Domain and Custom Domains
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