V1 devices separate the array from the device and return the Custom ID and Card ID separately.
On the other hands, V2 does not detach it from the device and returns the original array, not separated ones.
That's why custom ID part is not implemented in SDK V2 as well.
Still, if you are using SDK V1 and SDK V2 together, you will want to make it happen in V2 too.
For your reference, I attached example code from BioStar 1 - BS2_ScanCard_in_BioStarCodes.cpp
Please find details how to separate the array and apply the same logic in SDK V2 integration.