Hello talia285,
We understand you're encountering issues with Snapchat being accessible on your child's iPhone during downtime. We certainly understand the importance of those app limits, and want to do everything we can to ensure we get this rectified.
To begin, have you verified all of the Downtime/App Limits are set up correctly for Snapchat, and that the Block at Downtime/Block at End of Limit features are enabled for the affected family member? Be sure to double-check those settings, using the article here:
Use Screen Time on your iPhone, iPad, or iPod touch
Specifically, be sure to check the "Set a Screen Time passcode" section, under Step 4.
If everything looks OK there, be sure that you've tried changing the Screen Time passcode as well, via those same steps under the "Set a Screen Time passcode" section. Also, be sure to check if your settings are syncing properly among all impacted devices, and ensure that they're fully backed up, and running the latest iOS version, using these steps:
Update your iPhone, iPad, or iPod touch (begin with the "Before you update" section if you're not running the latest version)
Lastly, if the issue persists from there, let's try toggling the "Ask to Buy" feature Off/On on your device to see if that helps, following this article:
Request and make purchases with Ask to Buy
Be sure to refer to the "How to turn Ask to Buy on or off" section.
If, after everything, you still encounter this specific issue, be sure to reach out to our AppleCare support team, using this link:
Contact Apple Support
We're confident that if those steps don't rectify this issue, our AppleCare support team will help get to the bottom of this.
Take care!