Reg. required on CM305!

Hi

I’m new to Flightware,this being my first post.
I’m hoping someone can help.
I’m trying to find out the Registration of 737-700 of
COPA Airlines flying from IAD-PTY today.
I’ve tried planefinder and Flightradar24 but to no avail.
Does anyone know where I might be able to find out?
Thanks in advance.
Pete