A case of human error that is easily solved by RTFM or RTSL (read the source Luke).
Required endianness is clearly commented per key in essential examples included with the LMIC library (and in LMIC-node).
Different libraries/platforms require different endianness, that is why the TTS Console provides options to view/copy the keys in different formats.
Bolting on extra code on the end device side to check if the keys are in correct order only to solve an RTFM issue is not very useful.
More useful would be when the TTN Console provides an option where the user can select a format for the keys to be shown by selecting the name of the library/platform used.
You can add an issue with a feature request for this on the TTS GitHub repo if you would like to have such feature.
Also see: Format of Keys and ID's for Arduino LMIC libraries [HowTo]