HP Elite X3 on ATT prepaid network

At&t may be rejecting non VoLTE phones. These unlocked phones will work on AT&T 

https://www.google.com/url?sa=t&source=web&rct=j&url=https://www.att.com/ecms/dam/att/consumer/help/pdf/Service-Capabilities-Unlocked-Devices-ATT-Network.pdf&ved=2ahUKEwiX-Jv8oYLtAhXQo1kKHYhHDGcQFjAAegQIARAB&usg=AOvVaw3sCP2kJRUevj0ARWKoc1nJ

I am getting a SIM missing or Invalid error. It does recognize the sim is in there though as I have dual sim trays and it will "see" that there is a sim in either tray.

How can ATT not service a 3 year old phone?
I'm not familiar with VoLTE.

It even recognizes ATT as the carrier but wont receive any signal.

@lizdance40 @ATTHelp 

Did you try the other sim slot?  
Replacing the sim sounds like a possibility, but it may also be your account is not provisioned correctly.  

It seems unlikely, but your phone may not be compatible with AT&T. 
Volte stands for voice over LTE. Do you have to have a phone off of AT&T‘s list that is voice over LTE compatible on their network.  
When 3g is shut down, (it may be already in your area) Any phone not VoLTE capable won’t work.  
well AT&T’s stated shut off date is February 2022, there are areas that have already been shut off.

@lizdance40 

Ah.

Yes it recognizes that there is an ATT sim in either tray. It just gives an invalid or missing sim error and cant get any signal. However, it detects that there is a sim and specifically an ATT one in whichever tray I put it in.
The account is the prepaid unlimited 65$ plan, but it should be provisioned correctly seeing as I updated the IMEI in my account on the ATT page.

I'm not sure about VoLTE but the phone is capable of 2g/3g/4g in the settings.

I have no other phone since my iphone broke but the sim worked fine in the iphone a day ago before the screen failed.

The phone itself (the HP) is an unlocked ATT phone which I bought directly from HP.

The phone was released in 2016-2017 and marketed towards ATT business accounts. 

I did use it on the more standard contract plan as opposed to prepaid if that matters.

I'm just kind of shocked that a 600-700$ phone from 2017 is already being removed from service if that is the case.

The sim I have is compatible as the iphone and the HP both take a nano-sim.

Not sure how to proceed. I have fully updated the HP, tried both sim trays, factory resets, updating the IMEI in my account, etc.

Thanks @GLIMMERMAN76 

That was the answer I was a afraid of but suspecting.

The fire phone and Red Hydrogen One were dead and unsupported right after the warranty expired in one year.

Your phone doesn't have VoLTE in the notification bar, you'll need to replace it. 

An old thread. 

https://forums.att.com/conversations/other-phones-devices/hp-elite-x3/5defda64bad5f2f6068c15ab?page=2

Do not buy the new duo screen.  Already problems with replacement devices, warranty etc.  Too bad.  I thought it was a much wiser way to do a dual screen phone than folding screens