Gem not accepting supports even though the requirement has been lowered.

I picked up a reap staff, decided to throw some supports in it and realised I couldnt. I can use reap just fine, but socketing supports into it are impossible.




Other things of note are: Without my weapon swap, I do not have the intelligence required to use the staff.
The error message trying to socket the support gem says:
Warning:
- This Support cannot be socketed into this skill
even though Brutality and Reap should be compatible, the tooltip says they are. Additionally, all the other support gems in the game are greyed out in the cutting UI.