Old iPhone 8
Will erasing my old iPhone 8 also erase the information already transferred to my new iPhone 13? Also, can I only get a card for the trade-in? Why not cash?
iPhone 8
Question marked as
Erasing the iPhone 8 will not affect the iPhone 13 - assuming you carefully perform the cleansing of the iPhone 8 without disrupting iCloud.
What to do before you sell, give away, or trade in your iPhone, iPad, or iPod touch - Apple Support
You receive a card instead of cash so the value of your Apple device is used for future Apple product purchases.