Hi Adam,
Re: How does 'Ask to Buy' work for App Store purchases?
See how to: Approve what kids buy with Ask to Buy - Apple Support
Eg: says: "If the family organizer approves the request and completes the purchase, the item automatically downloads to the child's device. If the family organizer declines the request, no purchase or download will take place. If a child redownloads a purchase, downloads a shared purchase, installs an update, or uses a redemption code, the family organizer won’t receive a request".
Re: "my mom got me the new iPhone 16 Pro Max and I accidentally used her card and
she turned on ask to buy in the App Store can I still pay for it with it being on "
Apple requires a payment method is listed in your account for the first time you use the App Store or iTunes,
even if you only download free apps etc.
You may need to pay your Mom, as it seems the family organiser has to ok and complete any purchases.
Above linked article also says: "If a family member turns 18 and the family organizer turns off Ask to Buy,
the family organizer can't turn it on again".
If or when your Mom turns off "Ask to Buy" for you:
To accept the responsibility for your purchases, you would need a payment method on file in your Apple Account:
See below for what payment methods Apple can accept in your country or region:
Payment methods that you can use with your Apple ID - Apple Support
and
See how to add an Apple Account payment method:
Add a payment method to your Apple Account - Apple Support
All the best :-)