Hi Apple-ab-user,
Seems you have a long-standing problem with "Ask to Buy".
The many families who have it working properly likely do not say anything much.
Seems it can be set up smoothly in many cases.
Much as we;'d like to help: as Apple users, like yourself, those in the Community here can not see how you have set up "Ask to Buy" or where the hitch occurs, eg: whether you have set it up on one device only, or on several devices you use, whether there are other restrictions set, (either on your device, or children's devices), that limit purchases, whether your children have their own Apple IDs, whether there is an older device that has pre-"Ask to Buy" settings over-riding purchases made in error by smaller children, etc. etc.,
Apple support's online article offers trouble-shooting tips.
If Ask to Buy isn't working - Apple Support
or
How to Approve what kids buy with Ask to Buy – Apple Support
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Other articles that may be worth investigating / checking settings etc.:
Manage App Store purchases, subscriptions, settings, and restrictions on iPad – Apple Support
Use parental controls on your child's iPhone, iPad and iPod touch – Apple Support
Use Screen Time on your iPhone, iPad, or iPod touch
Prevent in-app purchases from the App Store - Apple Support
Set up Screen Time for a family member on iPad - Apple Support
All the best :-)