Trouble sending serial data to old iMac running a terminal emulator

I’m trying to get my Arduino to print text on the screen of an old iMac G3 using the Serial library. Currently I’m trying to use Zterm 1.7b on the Mac, but I think it is not finding the USB port, or there is some other configuration error. Nothing shows up in the terminal window. I’ve matched up the Baud rate to the Arduino. 8 data bits, no parity, 1 stop.

Any suggestions for other terminal emulators for a Mac running OS 9?

Anyone else ever successfully use Zterm on an OS 9 machine? If so, any tips?