Adding a second email to a Custom Domain

Hello,

I have subscribed to iCloud+

I have added the feature for email via a custom domain.

It is working fine for one user.

Now I want to add an email for someone else who will be using that custom domain.

The second user is part of my family sharing.

I added them as a second user on my iCloud - Custom Domain.

They received the email saying

"A family member set up the domain “xyz...zz.org” to work with iCloud Mail. To add your own custom email addresses to that domain, please go to iCloud Settings."

When I go to iCloud Settings I see the options below. That is, it includes the option for

"Custom Email Domains".

But when she goes to iCloud Settings the equivalent menu is WITHOUT "Custom Email Domains":

We can't see any other way to create the Custom Domain email address.

Are we looking in the wrong place? Or what could have gone wrong?

How is an invited user expected to setup a custom domain email address?

Some things that might be relevant.

• we only set up her Apple Id and iCloud mail account a few hours ago.
• similarly we made her account a member of my family group recently.

Does family-sharing need to be setup so that the other member has "share purchases" enabled in order for her to access a Custom Domain? I think I unticked that when setting up Family Sharing settings.

Any insights from someone who has got through this would be very welcome.