Hello and welcome to Apple Support Communities, PaulBla!
We understand you're trying to add a card to the Wallet app on your daughter's iPhone, but you've been unable to. We'd be happy to provide information about what's happening.
In the following article, at the bottom of the page, you'll see that if the user is under 13, Apple Pay is not available: Set up Apple Pay. If your daughter is 13 year of age or younger, this would be why you are running into this error.
What you can do is set up and use Apple Cash for members of your Family Sharing group that are under 18 years old. Below we've quoted the steps you can take to do this, which are found within this article: Set up and use Apple Cash Family
Set up Apple Cash for a child or teen
1. On the family organizer's iPhone, open the Settings app.
2. Tap [your name], then tap Family Sharing.
3. Tap Apple Cash, then choose a child or teen.
4. Choose Set Up Apple Cash.
5. Follow the instructions on your screen to set up their account. You might need to verify your identity. If you see Pending, make sure your child meets the requirements.
After you complete these steps, you can view and manage the Apple Cash accounts of your children and teens.
We hope this clears things up.
Have a great day!