I can't turn off Find My iPhone

When I try to deactivate the option on the phone, it doesn't work, and when I log in from the website, I get this message:

"Cannot remove the iPhone. Do you want to prepare it for trade-in or repair?

This iPhone is associated with your Apple account and cannot be removed while it is online, but you can prepare it for trade-in or repair."

I just want to reset my phone from the Mac, but for that I need turn off Find My Iphone