Having trouble flashing a custom recovery onto my HTC one m8

I want to load CM onto my phone, but I am stuck on fastboot flash recovery recovery.img part

I have tried flashing it when it was locked/unlocked, and various other things, but always get this error

target reported max download size of 1830711296 bytes sending 'recovery' (0 KB)... FAILED () finished. total time: 0.001s

I don't know exactly why its not flashing, any help would be greatly appreciated

HELP lol