iPhone 6s Plus locked by Straight Talk

Walmart does not sell unlocked phones. The only source for unlocked phones in the US is directly from Apple.

You were sold a phone that's locked to Straight Talk. Only Straight Talk can unlock it. You will have to activate it on Straight Talk and maintain service there for whatever period they specify in order to be eligible for unlocking.

BTW, there are no for-fee third party unlocking solutions. There are temporary hacks to make a locked device function as unlocked. The hack will be deleted with any restore of the device, or even an iOS update will likely remove the hack.

As KiltedTim posted, the only way to get an iPhone permanently carrier unlocked is to ask the carrier it is locked to process an unlock for you. If you don’t meet their requirements for unlocking, then they won’t unlock it for you.

Hello!

Should not be a big problem to solve, let try one of these ways:

1. Restart your device's (iPhone and Mac).
2. Update iTunes to Newest Version (from the App Store, in the Updates section, check if is one for iTunes).
3. Delete Previous iTunes Backups (On the top bar, click iTunes and go in preferences, then Devices. Select and remove the backup you want to make space in your Mac).

If the problem persists, let me know or contact Apple support.

A.A.

I do not know how this answer get here.

Sorry...

No, it won't solve the issue of the OP's phone being locked to Straight Talk. Did you even bother to read the OP's entire post. See the response by Kilted Tim below yours.

I mean, I do not know how my answer get here. Sorry