SIM not supported in unlocked phone

I bought a Refurbished iPhone XS 256GB - Space Gray (Unlocked) on apple.com While setting up, I get to a screen that says

“The SIM card that you currently have installed in this iPhone is from a carrier that is not supported under the activation policy that is currently assigned by the activation server.”

I am really confused. The phone purchased is supposed to be unlocked.

What am I supposed to do?