Be careful not to invert polarity in the screw terminal or it may damage the board and even more.

Do not use the servo connector as an input or do it at your own risk.
Voltage input connected to general I/O pins may cause chip damage if it' higher than 3.3V .

(1) You will need to bend a fin and remove the pin of the TO-220 heatsink. Make sure the PCB has no bare traces underneath or apply an insolator before (i.e. piece of chattertone).

• Install bossac (version ≥1.8)

sudo apt install libreadline-dev libwxgtk3.0-*
git clone https://github.com/shumatech/BOSSA.git
cd BOSSA
make
sudo cp bin/bossac /usr/local/bin

• Prepare the firmware

cd ~/klipper
make menuconfig

make clean
make

• Flashing the Seeeduino XIAO Connect the Seeeduino XIAO to your raspberry if it's not already done. Get the port of the XIAO, i.e. ls /dev/tty*, and modify the default /dev/ttyACM1 in the command line bellow. Use tweezers or short lines to short the RST pins in the diagram twice. The orange LED lights flicker on and light up. Then send in the next few seconds this command line matching your port.

sudo /usr/local/bin/bossac -i -d -p /dev/ttyACM1 -e -w -v -R --offset=0x2000 out/klipper.bin

More informations on how to reset for flashing:
https://wiki.seeedstudio.com/Seeeduino-XIAO/#enter-bootloader-mode

See ercf_hardware.cfg

If you want to support my work: https://www.pcbway.com/project/shareproject/ERCF_EASY_BRD.html
note: default setting is "HASL lead free" but if it doesn't matter to you, just change this option to get more affordable boards.

Or just download the Gerber files and upload it to the manufacturer of your choice.