Why am I getting ''Invalid input'' error in the CLI of my DWS-302x and DWS-4026 when typing valid commands?

Some commands are not available in basic mode with low user permission and you will get the ''Invalid input'' error.
 

For example:  When you first log into the CLI, you will have User EXEC mode, the first level of access and very limited access.

You need to type ''enable'' to get into "privileged" mode. From there you can  find general system info such as firmware information by typing ''show version'' and the management interface IP by using '' show network''.
 

Please check the CLI manual for more info about command groups and level modes.