CLI doesn't accept decryption key

[sigram]

Here's the packet:
1501E0C8BC70CA52DD41812142B86316935B1E861DEE86611F9813CB861558FC98E8D0E5AD0E6479BD1D154EAF6083F76A774F09948A

The decryption key is 9cd8fcf22a47333b591d96a2b848b73f. However, when trying to specify it on the command-line it doesn't seem to work:

$ meshcore-decoder decode --key 9cd8fcf22a47333b591d96a2b848b73f 1501E0C8BC70CA52DD41812142B86316935B1E861DEE86611F9813CB861558FC98E8D0E5AD0E6479BD1D154EAF6083F76A774F09948A
error: missing required argument 'hex'

I tried various combinations of flags, at best the -k or --key flag is ignored if followed by other flags. But no combination results in accepting the key.

[sigram]

It turns out I used the wrong key :) and the syntax is either -k hex or --key=hex. Still, the error message is confusing.