Q: Terminal rejecting password

The password required here is the LOGIN password that is matched with your login ID, not the disk decryption password or the firmware password, or your Apple-ID password, or your iCloud password..

you may not be set up as an admin on your computer.  Open System Preferences, then select the "Users & Groups" panel and then your user.  Now check the box "Allow user to administer this computer"

Hello ! Dr . Mark

       I have seen you screen shot you are trying to execute sudo command , and it is not excepting by entering your login password or to say user name password .

To run sudo command root user account must be created and from there it is to be executed , after completing the task , please log out from the root user account .

Suggested articles : Mac OS X: sudo command requires a non-blank admin password - Apple Support

                               : Enabling and using the "root" user in OS X - Apple Support

                               Thanks !

You do not need to enable the Root User to perform sudo commands, and I recommend you do NOT do that.

Having the root User enabled leaves your Mac much more vulnerable to being hacked, and does not improve your ability to use the Sudo command.

tygb wrote:

 

To run sudo command root user account must be created and from there it is to be executed

This is blatantly false information.

Dr. Mark wrote:

 

However, the password entered indeed is the password for my computer.

I am using my Login password, the same as I use to log on to my computer.

Verify your caps lock is not on.