If you want to follow the guide, make sure to read through some of the later posts for some updates on the method. You do NOT need the custom firmware anymore, just make sure you’re on a recent version, 1.18.2 is fine.
As for the error, it sounds like an odd one I haven’t seen, I will definitely need some images. To upload images, press this button;
@Thorus Use the base GRBL, that’s what even the official snapmaker profiles use now. I discovered this in my post here;
The only caveat is if you’re using the rotary, then you’ll need to use the Snapmaker profile.