Sprint iPhone x. Apple store purchase. ?unlocked

The message you're getting indicates the phone is NOT unlocked. If your friend paid full price for a Sprint phone from Apple, then your friend will have to contact Sprint and request an unlock. In order to do so, Sprint will require that the phone be active on their network. Sprint are the only ones who can authorize unlocking it.

Sprint is more complicated than other carriers. First of all, you cannot insert an activate Sprint sim--it does not work that way.

If you want to have the phone unlocked you will need to activate it on Sprint and request an unlock in accordance with its policy (50 days).

At the moment Sprint is offering a year of free service and you might be able to accomplish the unlock that way at very modest cost. There are other approaches that might work with Sprint but there is less certainty.

Unlocking your Sprint device

However, by far the best option, would be to return the phone and get the model you want.

All iPhone X models are not unlocked which is why you must select a carrier. Apple is selling an unlocked version in the US and some other stores. A T-Mobile version is supposedly easier to get unlocked than the other versions.