Are you using an older version of mIRC?
This was discussed in depth in this topic:
https://forums.mirc.com/ubbthreads.php/topics/244052/Connect_to_networksKhaled mentioned using the 'password' field for lookups in the future, I don't know if it was ever added.
I do believe there's a solution to your problem in this topic though, so please take a look and I'll try to reproduce your problems later if necessary.