Here is the first sim never lock post, I'll be showing you how to fix this sim not a valid problem on your iPhone. This is using iPhone 7 which is locked to teach you how to fix that and unlock the phone.
Here is to tell you how to unlock an AT&T locked iPhone. This is an official way, this way as you were asking AT&T to unlock your phone, an official AT&T to unlock your phone is not that an efficient, like the wake, like jailbreak also.
You can use any company's SIM card
To use this method you need to fulfill a certain kind of requirements and listed right here. If you have included this requirement then in most of the cases then you'll be able to knock to officially.
What I mean by unlocking official is you can use any company's SIM card to use your iPhone, there will be no limitation that you can only use AT&T SIM card on your iPhone, and I actually work this with my iPhone 3GS, which is a very old iPhone, but it works pretty fine, and it works well and really used.
Reuse another company SIM card
I've been reuse another company SIM card to work with my phone, so there's an official way. Probably you are using it because it seems might more secure than you jailbreak your phone. If you fulfill this requirement you just go to this website and then you just click AT&T, one is custom I just know.
Then you type in your IMEI code if you don't know IMEI code you can just solve this, and then they will give you an idea micro, just like SMS to your iPhone, and then you just tap it in, and then I do not report and then go.
Then you will be able to get an email from AT&T, like three to four days, like two working days, and then you will be able to not your iPhone, and I kind of know my iPhone for free GS before. But I can do it now, there is also a post to prove that I can do it.
The steps of activating your phone
If it didn't unlock the phone then when you reach to this page you just said that the same cousin of functioning or you need to contact your mobile provider, but right here you just click the language location, and then the Wi-Fi, and then you're activating your phone, and then just wait for a second and then activate it.
Then you just set up like the location of stuff is turn it down, and then set up a new iPhone, you choose your option, I set a new iPhone and then maybe app want e type in the night, and then yes, basically just activate and in terms of condition you sick ok, no stereo standard, next okay, and then thank you, you can use the iPhone.
It's an activated not jailbreak, officially activated adopted by AT&T. I hope you enjoyed this post.
Other web page resource
How to unlock your iPhone on AT&T | iMore: https://www.imore.com/how-unlock-your-iphone-att