I assume you are trading in direct with Samsung. I've just done the FDR for my trade INS and have had no issues.
If you are doing carrier, they all are different. The last time I tried trading in with Verizon buying online the store told me I had to use the box they send and mail it in. The other times the store took the trade in and gave me a receipt for the value if trade in. With Verizon it's hard to tell what they do from day to day, they change their ways more then women change their minds.
Samsung direct or carrier trade in you will want to do the factory data reset and remove your SIM card if you're not reusing it and SD card if you have a SD card. Hopefully you have a spare phone to use as back up since you're trading one in. The note 7 fiasco should have taught a lesson, always have a decent back up, you never know when you might need it. You break your phone, have to send it in for repairs. I recently had to send my fold 2 in for repair, took week turn around, but I had my note 20U for back up, so I wasn't complaining that I didn't have a phone to use. If you don't have a back up, this could be a time to create a back up phone.