SIM Not Supported

I've just bought this iPhone from UK to the Solomon Islands and this is what came up after "slide to set up"

SIM Not Supported

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. This is not a hardware issue with the iPhone. Please insert another SIM card from a supported carrier or request that this iPhone be unlocked by your carrier. Please contact Apple for more information

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Try Again

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iPhone SE

16G

Model A1723 EMC E3042A

Please help.

D T