iPhone 6s 32gig storage

iPhone 6s 32gig storage S/N : DNQRX2RJHFLR lock screen password is : 123456 installed 15.8.4 Audio Bluetooth Wireless Camera all tested and working battery is at 68 % at the moment I just put my 02 sim card inside I get the message sim not supported. so don't know how to fix this not sure what network the phone was originally on .

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