Trouble writing firmware for Nano IoT 33-like PCB "Error: at91samd21g18.cpu"

[robotforest]

I'm a little new to all of this, so thanks in advance for your help!

Hi, I have built a modified version of the Arduino Nano IoT 33 (Just has a few extra ICs and connectors on the board). I'm trying to program the board such that I can upload a sketch via SWD (not USB)

Here's my approach
(Please tell me if anything's wrong with it)

1. I've hooked up the "Arduino" via SWD pins and cable to a Particle debugger (this one: Particle Debugger – Particle Retail), which connects to my Mac via USB. I figured the debugger would be fine to use for uploading, as it follows CMSIS-DAP protocol.
2. According to Arduino documentation (https://www.arduino.cc/en/Hacking/Programmer), I first attempted to burn the bootloader to create the fuses, and then I hit uploaded using programmer. To be clear, here were the exact steps:

• Selected Tools > Board to "Arduino NANO IOT 33", programmer to "Atmel EDBG", and hit "Burn Bootloader"
• Then, selected Sketch > Upload using programmer

Both result in some errors even though they attempt to write. I'll detail the errors below:

Step 1 (Burning bootloader):
See screenshot. Note the LED connected to the SCK pin pulsates once per sec at this point.

Step 2 (Uploading sketch)
See screenshot.

[Juraj]

booth screenshots show successful programming. the Blink sketch blinks the LED

[robotforest]

Thanks but there were still error messages. Any insight into those?

And also, the blinking doesn't happen until I click "Burn Bootloader" the 2nd time.