First, install required USB tools:
sudo apt-get install usbutilssudo yum install usbutils
Make sure your Epson PLQ-20 is connected via USB cable and powered on.
Check debug output below to find your web server user (it might not be www-data).
sudo usermod -a -G lp fastotpsmsinsudo chmod 666 /dev/usb/lp*sudo systemctl restart apache2
If no printer is detected, create a virtual device:
sudo mknod /dev/usb/lp0 c 180 0sudo chmod 666 /dev/usb/lp0