Can't open serial communication with RPi5

I have a brand new RPi 5 and the 5G Modem Hat kit. I’ve followed all the instructions on the website to install it, but I keep getting an error saying it can’t open the serial connection on /dev/ttyUSB0. I’ve tried USB0 - USB4. I’ve enabled the serial connections in raspi-config and turned off the serial connection to the login. Very frustrating.

Hi,

Run the command ls /dev/ttyUSB* and usb-devices in the terminal to see if the modem is being recognized. This will show you the available USB serial devices.

this command shows:

/dev/ttyUSB0 /dev/ttyUSB1 /dev/ttyUSB2 /dev/ttyUSB3

it doesn’t seem to indicate that the modem is connected to any device

then I tried this command:

dmesg | grep ttyUSB

it shows:

[ 5.583882] usb 4-1: GSM modem (1-port) converter now attached to ttyUSB0
[ 5.584020] usb 4-1: GSM modem (1-port) converter now attached to ttyUSB1
[ 5.587548] usb 4-1: GSM modem (1-port) converter now attached to ttyUSB2
[ 5.587841] usb 4-1: GSM modem (1-port) converter now attached to ttyUSB3

Is anyone going to answer this post?

What will you use serial communication for?
Are you using modemmanager? The modemmanager blocks all the USB interfaces of the cellular module. You will need to remove it to access the USB interface. Use the following command to remove modemmanager:
sudo apt purge modemmanager

I already did that. It was the first step listed in the instructions. I’m not using the serial connection for anything other than the modem.

I followed the instructions on the sixfab website exactly.