in app purchases aren't allowed

Unfortunately, the Apple TV app doesn’t support in-app purchases on Fire TV at this time. You will have to do the transaction (subscribe, buy, rent) on a different device. Once the transaction is done, you can view that content on Fire TV as well.

Get the Apple TV app or Apple TV+ app on your smart TV, streaming device, or game console - Apple Support

2. On Amazon Fire TV devices, you can't purchase content from the Apple TV app. You can purchase content on another supported device to watch it in the Apple TV app on your Amazon Fire TV device.

You have screen time restrictions on:

Use parental controls on your child's iPhone, iPad, and iPod touch - Apple Support

You see how to turn it off and on under

"Prevent iTunes & App Store purchases"

And then turn on in app purchases

Good luck!

On what make and model TV do you have the Apple TV app? Would that perhaps be Fire TV?