When you order iPhone or iPad from Amazon, eBay from oversea or purchase from USA as “sim free” and travelled out side the country, you could locked in to the SIM Not supported situation.
Apple distribute iPhones and iPads under US Reseller Flex Policy, that means when you purchase phones from a store like Best Buy or Wallmart the sim free version will need you to activate the phone using a US sim.
I recently ordered an iPhone and it wasn’t an unlocked phone. It is setup on the US Reseller Flex Policy. It looked like it was purchased at Best Buy “sim free”. I could not activate it with an international SIM Card.
You need to find someone with a US SIM card to install durning the activation process. Once it was activated with any career you’ll be able to install the international Sim Card and everything will work.
If you are looking to purchase one of those phones internationally make sure you have a US sim card to go through the activation process, or research the US Reseller Flex Policy.
Similar issue reported here and you can learn more information form that post too.