I don't use ZNC, so I don't know for sure what's the problem.
But this behaves as if you mis-typed the password. It looks like ZNC requires you type a very long password string there, so if it's not 100% perfect then it's wrong. The server dialog doesn't give you the option of seeing the password as you're creating it, so let's try having you creating your password again, only this time do it a little differently.
Open NOTEPAD and create the username/network:password string in NOTEPAD where you can see what you're doing.
Next, highlight the string with your mouse, and then press Ctrl+C to copy it into your clipboard.
Next go to the MIRC server dialog and PASTE the string into the password field, then save it.
If this works, you must have made an error when you typed it the 1st time.
If it still doesn't work, check your messages window where you're now seeing the message demanding you send the password - are you seeing any other error messages preceding the one telling you to use quote-pass?
edit: if still having trouble, try coming to networks like libera.chat where ZNC has a channel, or ask in the mirc channel there
Last edited by maroon; 21/01/22 11:50 PM.