Well, if you have obtained the Starlight Keyblade code from KHUx, it finally can detect, but have to wait till 29/1/2019 to redeem the Starlight keyblade code (Message says the voucher is no longer valid).
If u are from Southeast Asia (Malaysia, Singapore, Indonesia, Thailand) and have/are planning to buy the R3 Asia English copy of KH3, create another PSN account and set to US, then the code will work. The code won't work on R3 Asia PSN accounts.
This is when I'm trying to redeem using my R1 US account (2nd PSN account):
And this is when I'm trying to redeem on my R3 Asia account that is set to Malaysia (my main PSN account):
For Southeast Asian players, see how to redeem the Starlight Keyblade code: