Below is the exact, copy-paste fix for your error on macOS (Arduino IDE 2.x).

The core issue is wrong port + wrong baud rate — the HexBright is not on /dev/cu.usbserial-0001 and does not use 19200 baud.

1. Find the real HexBright port

1. Unplug everything except the HexBright.

2. Open Terminal and run:

   ls /dev/cu.* | grep -E 'usbmodem|usbserial'
   
   

3. Re-plug the HexBright (wait 3 seconds).

4. Run the same command again.

   You should see a new line appear, e.g.:

   /dev/cu.usbmodem14101
   
   

   → That’s the real port.

   (If nothing new appears, try a different USB cable — it must support data, not just charging.)

2. Force the correct port + baud rate in boards.txt

1. Open your boards.txt file:

   ~/Documents/Arduino/hardware/hexbright/boards.txt
   
   

2. Replace the entire content with this exact version (fixes baud + port detection):

   #####################################################
   hexbright.name=HexBright
   
   hexbright.upload.protocol=arduino
   hexbright.upload.maximum_size=30720
   hexbright.upload.speed=57600
   hexbright.upload.tool=avrdude
   
   hexbright.bootloader.low_fuses=0xff
   hexbright.bootloader.high_fuses=0xde
   hexbright.bootloader.extended_fuses=0x05
   hexbright.bootloader.path=optiboot
   hexbright.bootloader.file=optiboot_atmega328.hex
   hexbright.bootloader.unlock_bits=0x3F
   hexbright.bootloader.lock_bits=0x0F
   
   hexbright.build.mcu=atmega328p
   hexbright.build.f_cpu=16000000L
   hexbright.build.core=arduino
   hexbright.build.variant=standard
   
   

3. Save & restart Arduino IDE.

3. Select the correct port in IDE

1. Tools → Board → HexBright

2. Tools → Port → /dev/cu.usbmodem14101 (or whatever your ls showed)

   Do NOT select /dev/cu.usbserial-0001 — that’s a different device.

4. Test with Serial Monitor (no upload)

1. Open Serial Monitor (9600 baud, No line ending)