error on connecting port 5432

Hi,

When I m creating a test db user using below command using root OS user
sudo -u postgres createuser -p 5432 --pwprompt testuser

I am getting the attached error of port.

But my postgres services are running fine on port 5432, I am sharing
the screenshot of that also.

So please help me in letting me know why I am getting the above error
when I am connected to the root OS user?

Note - I am able to create a test db user when I am connected to
postgres using psql command.

Regards,
Atul