(adsbygoogle = window.adsbygoogle || []).push({}); Go onto their region version of xbox.com, sign in then redeem from there
for example:

If you are in the US and what to redeem a UK code go on:
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AND

If you live in UK and want to redeem a American code go on:
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AND

Ireland go here:
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hope this helps!

Feel the sarcasm!

I have redeemed US codes on my friends UK account before

it works.... thing is, you can use the same code in 2 different regions