I have also been turned down for iPhone 12 Pro Max. I have a near impeccable Credit Score with Experian (used by Barclays), no defaults ever etc etc. I have checked Trans Union (Credit Karma - used by Barclays). Also good. There is no negative CIFAS information.
Perhaps people must have a Credit Score of 999/999 AND a private yacht? I don't have a yacht. Or an iPhone 12 Pro Max it seems.
I have appealed to Barclays as their front line agent could not see a valid reason given the Credit Score information. I also informed Apple. I have never been turned down for credit.
Something is very wrong. This affects the reputation of Apple, I think. And will not help sales!
I accept that Barclays can choose who to give credit to, but this appears to be a very poor choice of Finance Partner for Apple.