Hi
It sounds like you're having an issue with the Ask To Buy feature. If so, you started from a great resource: Approve what kids buy with Ask to Buy
As mentioned in the article the steps below you may also need to turn off Require Purchase Approval.
"How to turn on or turn off Ask to Buy
If you're a parent or guardian, use your own device to turn on or turn off Ask to Buy.
On your iPhone or iPad
- Open the Settings app.
- Tap your name.
- Tap Family Sharing.
- Tap your family member's name, then tap Ask to Buy. In iOS 15 or earlier, tap Ask to Buy then tap your family member's name.
5. Turn on or off Require Purchase Approval. "
If you've completed these steps and the issue continues, ensure both devices are running the latest iOS update, complete a normal restart and test again.
Should the issue remain, reach out to Apple Support directly to further assist. Get Support
Best.