Hello Aw_阿歪,
We see you're having issues when trying to get ready to place an iPhone 13 order, and we can help get that headed in the right direction.
To help rule out issues with the connection, try using a different one, if possible. For example, if you're on cellular data, try connecting to a strong Wi-Fi network. If you're already on Wi-Fi, try cellular data instead, or a different Wi-Fi network.
If you happen to be using any kind of VPNs or other networking/security apps, try temporarily uninstalling them.
It can also help to try a quick restart: Restart your iPhone
Also, if you have access to any other devices, see if you're able to complete the process from there.
If none of the above helps, you may try reaching out to Apple Support for ordering issues: Contacting Apple
Take care.