Setting the breakpoints actually works, but they aren’t properly registering internally (which also means you can’t remove them), This was fixed in #168, but there hasn’t been a new release since then. If you need this functionality right now, try checking out Gallium (and proably some of it’s dependencies).
Thanks for pointing that out. But it seems that my problem is more than just “improper registration of breakpoints”. Because the debugger never stops there, implying no breakpoints at all. I suspect that there are something that I missed when using Gallium, e.g. missing quotes etc. Am I using the command correctly?