iPhone upgrade reservation

I’m trying to reserve my iPhone, I’m eligible under the upgrade programme and am able to choose the model and store from which I wish to collect the phone.

Apple then asks me to sign in again and the process includes two step verification and I get the 6 digit number and enter it.

I then keep getting a message to say my session has timed out despite there being no hesitation or delay. Signing in again just repeats the issue, even on a different device. Any ideas?