Today I bought an iPhone X and tried to restore my iPhone 6s backup to it but failed. I got error message saying backup corrupt or incompatible. I was wondering if it was related to my carrier transfer from at&t to verizon but it turned out it’s not related. It is because the iOS on my iPhone X is older than the one on my iPhone 6s. After I upgraded iOS of my iPhone X to the latest version, I was able to restore it.