This is from Youtube automatic subtitle, so I'm not sure it's a correct sentence though.
못할 수도 있지. 되게 뭐라고 하네.
is a correct sentence that's colloquial and friendly sounding.
To break it down:
1. 못할 수도 있지
"못할 수(도) 있지" is a common phrase for saying "It's okay." in English, and that's usually spoken when you forgive(or be generous towards) someone who couldn't carry out his/her work well.
So what it means is kinda like, "It's okay, although at the moment you might have not done something well or even made a mistake."
These are some similar expressions:
- "(잘) (하지) 못할 수(도) 있지"
- "실수할 수(도) 있지" (Everyone makes mistake.)
- "그럴 수(도) 있지" (It happens.)
2. 되게 뭐라고 하네
"되게 뭐라고 하네." - This means "You nag too much."