Easily checked indeed:
Format of Keys and ID’s for Arduino LMIC libraries [HowTo]
Above holds for both for Classic LMIC and MCCI LMIC.
I simply don’t know if your LMIC library uses MSB or LSB for ABP.
If the LMIC library used is different than Classic LMIC and MCCI LMIC then I would suggest to use and test with either of these libraries in the first place.
For information about naming see: Arduino LMIC library naming: Classic LMIC and MCCI LMIC [HowTo]