Unable to complete pre-approval before preordering

The Apple website allows you to obtain pre-approval for their financing options before pre-orders start.

However, when I attempt to complete this process and have to type my credentials in to access my carrier account, I am met with a message “We’re sorry. Your existing rate plan isn’t an eligible iPhone plan. You can contact your carrier to keep your current phone number. You can also create a new account at an Apple Store”. This prevents me from continuing the pre-approval process.

I have verified that my carrier number and pin are correct. This is not the issues.

Any suggestions as to why I would be receiving this?