This is a niche issue/bug, and one that I had a nightmare attempting to explain to a One NZ team member via online chat.

It seems that the sign-in form (and registration form) at https://one.nz/#sign-in does not recognise certain top-level domain names, and uses Javascript to disable the Submit button when it thinks the email address entered is not real.

I discovered this today when I changed my email address from my old .nz domain name to a new domain which ends in .digital. I did this via the online account portal (which I'm now unable to sign into without the workaround mentioned below). The One NZ app is fine and doesn't have an issue with the .digital email address.

Is there anyone here who might be able to pass this on to the web team at One NZ?

The workaround in the meantime is to use developer tools in Safari/Chrome to remove the "disabled" attribute from the submit button, as well as remove the CSS classes that disable the button. You can then sign in easily. But, I don't want to have to do this every time I sign in to manage my account/bills etc.!