I ported "QR Decoder" plugin for C3! See this post:
https://www.construct.net/en/forum/extending-construct-2/addons-29/plugin-qr-code-decoder-51533/page-3#forumPost992435
It's my first ever ported plugin, not sure if everything is done correctly, but it seem to be working fine.
Have been trying to get this to work for hours now....
I am replying for anyone who is having the same problem as me!
Turn off "Use Worker" in advanced inside of CS3
or it will not work.
Best of luck
PS: Thank god i got it working. was about to have to buy a new screen XD