iPhone won't connect to the internet after removing the SIM card.

I have been told in the past that an apple phone can connect to the internet without requiring a SIM card as its essentially an iPod without it. I recently changed phones and have been trying to reset my old iPhone so i can sell it/trade in. However, it won't connect to the internet for me to go through with that process (as it needs to to verify for iCloud and necessary permissions and what not). It says it's connected to my WiFi and i have no issues with it or the router, but it still doesn't load anything or work, it just gives me the 7005 error message. I've attempted to restart the phone, disconnect and reconnect, and restart the router but nothing seems to work.

What am i doing wrong?