Q: I'm doing exactly as the instructions say, but I do not get a message saying "Congratulations, your iPhone has been unlocked". But, when under "Carrier" it says "Carrier 19.0". How do I know if it has been unlocked?

What did your carrier say when you requested the unlock?  Do you know if they've processed your request and provisioned the unlock?  Until your carrier sets it up, it won't work in iTunes.

Do you have your AT&T SIM in the phone and are you restoring it as a new phone in iTunes.

you will know it is unlocked when you get the message confirming it is so in iTunes after completing the restore as new procedure.

This the unlock procedure

How to unlock your iPhone for use with another carrier - Apple Support

and you should accept the carrier update that may well be the issue as it is the signature to the new Carrier

Sprint's policy is to refuse carry in phones. Have you checked with them about your plan?

Rstorm4 wrote:

 

I requested the unlock on AT&T's website and it was confirmed by AT&T. But the directions are different that Apple's directions for unlocking. I have tried everything and feel like I am getting no where.
I am trying to unlock this phone from AT&T (as it was confirmed by them) and once it is unlocked I want to switch it over to Sprint.

I doubt that you can switch to Sprint, because Sprint does not accept phones on their network that were not originally sold for use with Sprint. Call Sprint to verify that they will accept your AT&T unlocked phone, but I suspect the answer is No.