Good morning SophieCee!
It sounds your iPhone 7 is having some trouble signing in with your Apple ID. I’ll be happy to help out.
First, make sure that your account has no issue, and the Apple ID and password are correct. You can verify this yourself by visiting the Apple ID website here: Manage your Apple ID
If you're able to log into your Apple ID successfully, then try these steps for signing out and then back into your Apple ID on your iPhone: What to do after you change your Apple ID or password - Apple Support
Specifically, here's the steps:
iPhone, iPad, and iPod touch
If you’re using iOS 10.3 or later, go to Settings > [your name] > iTunes & App Store. If you’re using iOS 10.2 or earlier, go to Settings > iTunes & App Store.
- If you're signed out, enter your updated Apple ID and password.
- If you're signed in with your previous Apple ID, tap your Apple ID, then tap Sign Out. Then enter your updated Apple ID and password.
Restarting the iPhone and trying again may also resolve the issue: Restart your iPhone, iPad, or iPod touch - Apple Support