I get a "SIM Not Supported" Message when trying to install a new EE SIM card. Please help

[OldBlokesIPhone]

Hi,

I am moving to a cheaper tariff on EE and they have sent me a new SIM Card. 

On restarting my iPhone7 (which I originally purchased from O2, and with I still have the purchase documentation for), I receive a "SIM Not Supported" message and the only thing I can do is to re-insert my old O2 SIM card.

Can someone clever help me please?

[madasaf1sh]

@OldBlokesIPhone 

The iPhone 7 will probably be locked to o2 as it was released in 2016 so you need to follow this guide Guide: Unlocking an O2 phone to use a different SIM card 

And when you get confirmation that it is done you will need to plug it in to iTunes.. 

And to be fair the iPhone 7 is so far out of support, from and OS level and App level, it might be time to upgrade