ATT unlock phone

i will be traveling abroad and have an internationalSIM card I will temporarily be using for my trip. I had called AT&T to unlock my phone. They told me it’s unlocked and that I have to restore and then backup my phone again to complete the Unlock. Is this step still necessary or can I just enter the SIM card? On the Apple website it says if u are using a SIM card other than your carrier u just insert it. I read on a couple threads that the newer models don’t require I restore to complete the unlock. I have an iPhone 8 btw