C:\Android\com>htc_fastboot flash sp1 ..\partitions\splash1.nb0
htc_fastboot v3.0.9.2 (2015-05-29)
target reported max download size of 536870912 bytes
sending 'sp1' (7296 KB)...
OKAY [  0.160s]
writing 'sp1'...
FAILED (remote: Not allowed on PRODUCTION device)
finished. total time: 0.162s
htc_fastboot finished. total time: 0.259s

C:\Android\com>htc_fastboot flash sp1 ..\partitions\splash1.nb0
htc_fastboot v3.0.9.2 (2015-05-29)
target reported max download size of 536870912 bytes
sending 'sp1' (7296 KB)...
OKAY [  0.166s]
writing 'sp1'...
OKAY [  0.002s]
finished. total time: 0.168s
htc_fastboot finished. total time: 0.256s