The promotion really wants to be done over the phone, which helps with region verification.
Physically advertised on Pringles cans in the UK and EU, there's no actual purchase necessary: simply scan the QR Code provided on the UK or EU websites and click "Enter Game" to be taken to a new page with the Xbox promotion.
Despite saying a purchase is required, it isn't.
Upon registering an account, a code will be provided to redeem the prize. There does appear to be some amount of location checking to prevent users outside of the UK/EU from receiving a code, though no real verification makes it pretty easy to defeat and there's nothing stopping users from registering as many email addresses as they want either, making it very easy to acquire several codes to share with friends in other regions. These codes can then be redeemed on Battle.net by anyone, without any region checking or verification required.
Any player can redeem a code from anywhere, so share with your friends!
There are actually a total of four rewards available across a few different games, though the Crimson Bow Tie has not yet been datamined and isn't actually obtained until the Midnight Pre-Patch releases on January 20th anyway. Given that the promotion runs through May 5th, there doesn't seem to be much hurry either.
World of Warcraft in-game Crimson Bow Tie skin
Fallout 76 in-game Mr. Vault Boy Outfit and Mr. Vault Boy Mascot Head skin
Sea of Thieves in-game Scarlet Stack Sails skin
The Outer Worlds 2 in-game Julius P Canid skin
