A lot of SSHv2 key may not be accepted by our devices.
Indeed its lenght must be of 1024 bits and in OpenSSH format.
Puttygen which is widely used to generate keys doesn't uses these settings by default so just selecting ""SSH-2"" generating a key and saving it won't be enough.
So select the relevant size (1024) and export the generated key as on OpenSSHkey (see screenshot).
Then the generated key can be uploaded and used by the devices.