Sorry for the misunderstanding again, for my test i’ve used a different board to compile instead of the M0+ mentioned in the wiki. For your reference, i used Seeeduino Zero as my board. To install this board, you can add the following URL to the board manager URL: https://files.seeedstudio.com/arduino/package_seeeduino_boards_index.json
For more, to find out what serial of what board has, you can visit the github page to find such repo and its location, under variant.cpp. So for my test, I checked here: ArduinoCore-samd/variants/arduino_zero/variant.cpp at master · Seeed-Studio/ArduinoCore-samd · GitHub
You can see that it’s Serial1 and Serial2.
This caused some issues since we didn’t release schematics due to business aspect but we will consider!