Network unlocking A1661 iPhone 7 Plus From AT&T

Feb 19, 2009
The Woods of NY
Hey i have a question regarding network unlocking a iPhone... I picked up a A1661 iPhone 7 Plus off of marketplace for a client looking for their first ever iPhone and it was sold as "unlocked", but after trying my Verizon sim in it, it never gets past the activation screen with error says sim not supported, and looking under settings - general, it shows as sim locked. How do i go about unlocking a A1661 Iphone 7+ that was originally on AT&T. I tried the AT&T unlocking website, and it comes back as being on another persons account, and to unlock it they must remove it from the AT&T account. I called AT&T and because i do not know who's account or phone number its under they cant do anything for me. I made the assumption that since its a A1661, its automatically unlocked, and i did not look for sim lock when buying it. oops. I did try my back up AT&T sim in the 7 Plus, and it works perfectly, even though its a MVNO of AT&T, but the client has Verizon, so that will not do much good haha. Are these unlock websites any good? such as Should i even try, or start over from the beginning with another device, maybe one that's newer? I did update it to iOS 15 for 14.7, and it runs pretty well, but i cant imagine apple supporting it for much longer. Thank for your input. :)

Unfortunately I think that iPhone is a paperweight at this point. There is no way to remove those carrier locks. My guess is someone had AT&T and stopped paying on the phone and it will never be able to be unlocked.
AT&T does make you go through steps to unlock, which is sort of silly, but ...

I gave a friend one of out old i phones when his daughter lost hers. It was unlocked by me personally and they were never able to get it activated on Verizon anyway...

So it may be a moot point.
Seems like you missed the key step, as you mentioned, of verifying the phone works on your desired network.

If you cannot get it unlocked, maybe you could resell or offer a trade. I.E. see if someone has a Verizon and needs AT&T.
Update on this, i never did get the 7 Plus unlocked, so i listed it, and off it went. The client now has a iPhone XR and could not be happier.. the XR is a huge upgrade from the 7 plus, and it will supported much longer.