Hello st3tay,
Thanks for reaching out to Apple Support Communities. We see you have some questions about trying to use an app to trade in your iPhone, and we'd like to help. With application issues, on your iPhone, the following link may be able to help, as it walks through steps in what to do If an app on your iPhone or iPad stops responding, closes unexpectedly, or won’t open.
1) Close and reopen the app
Force the app to close. Then open the app to see if it works as expected.
2) Restart your device
Restart your iPhone or restart your iPad. Then open the app to see if it works as expected.
3) Check for updates
To see if updates are available for the app, open the App Store, tap your profile icon, then scroll down to see if updates are available. If updates aren't available for the app, update the software on your iPhone or iPad.
4) Delete the app, then redownload it
Delete the app. When you do this, you might lose data that was stored in the app. Then redownload the app. Then check to see if the problem with the app is fixed.
If this doesn't help, we'd recommend reaching out to the developer of the application for additional assistance.
How to contact an app developer - Apple Support
Regards.