Hello nanjayrich,
We understand that Ask for More Time isn't working as expected between your devices and your child's devices.
Do you have a Screen Time passcode enabled for your child's device? We ask because according to this support article: Use Screen Time on your iPhone, iPad, or iPod touch - Apple Support , "If you set a Screen Time passcode, Downtime includes an additional setting: Block At Downtime. When you choose this setting and you click Ask For More Time when Downtime starts, entering the passcode allows you to approve the app for 15 minutes, an hour, or all day. Child accounts can click One More Minute once, or click Ask For More Time to send their request to the parent account for approval."
If you haven't already, we recommend checking for any pending updates on you and your child's devices: Update your iPhone or iPad - Apple Support
If iOS is up to date and you have a Screen Time passcode enabled on your child's device, the next step is to reach out to Apple Support for a closer look. They have tools available to investigate further. You can reach out here: Get Support
Take care.