Hi Aka3262,
I had the same issue the past few days and finally figured out what to do.
Sign onto your AOL account through your computer.
choose your Name at the top right to get into your Account
"Account Security", scroll to bottom
"Manage APP Passwords"
"Iphone Mail"
Select your APP from the Dropdown list
click "Generate" in the blue box, a code will pop up, (write it down).
I then went into my Iphone and deleted the AOL mail from the phone so I could get a fresh start. Setup AOL again... Settings, Accounts & Passwords, Add account, choose AOL, here's the trick... when you go to setup the AOL account instead of using your regular AOL password, Use the Password that was Generated on your computer (the one you wrote down). Now you should be good to go!
Hope this helps!