IHS fees not showing for child application

[Yolouk]

Hello everyone.

I have just done my wife's application. I have paid and booked in for the biometric.

I am trying to do her daughter's application (17 years old). When it takes me to pay the IHS fees. It says under 18s are the reduced rate of £470 per year as I was expecting.

Then when I go through to next section. It says 0 usd fee
It says "exempt based on lead applicant being 18 or under Applying under visa route settlement - child or dependent of settled".
It generates a IHS number. And then asks me to pay for the visa.

Does anyone know why is this? It's really confusing me as it won't let me pay the fees.

Thanks in advance