I just sold an iPhone 6s Plus to someone. They get the message sim is not supported. The iPhone is unlocked. I requested it a year ago and it was approved. I requested it again for the hell of it right now and just for the email saying it was approved again in within 5 minutes. I’m assuming it replied fast because it was already unlocked. But still the same message. I put the imei number on swappa and it says it’s whitelisted and imei is clear and ready for activation. So everything is good. Could it be the guys T-Mobile SIM card? I don’t know. Any help would help.