Why my phone asked for passcode after I factory reset it and old passcode doesn’t work

Did you follow all of the instructions in this link→What to do before selling or giving away your iPhone, iPad, or iPod touch

luckenson209 wrote:

I donated it to a friend but she can’t use it because it kept asking for a passcode.

You have almost certainly come close, but not precisely stated the issue.

• “I factory reset my old iPhone, erase it from my account.” That is insufficient. Doing this failed to remove the iPhone from Find My, which is required. This is what needed to occur: What to do before you sell, give away, or trade in your iPhone or iPad - Apple Support
• “… it kept asking for a passcode.” Nope. Your Apple ID and password (not passcode) would be required to remove the Activation Lock left on your iPhone because you failed to perform the steps above.