Hi ahelgers,
Welcome to Apple Support Communities. We understand that you're having an issue with clearing your iPhone for trade in. We'd like to help.
When you are getting your iPhone ready, are you follow the steps found here:
What to do before you sell, give away, or trade in your iPhone, iPad, or iPod touch
Are you clearing the data on your iPhone by using the Erase All Content and Settings button or are you connecting to a computer? if you're having issues with one method, trying another method or changing the computer and/or network may help.
Let us know how that goes.
Take care!