- 잘 안 돼요.
- 잘 안 돼죠.
Sentence number 2 is incorrect because 어 is not needed to connect 되 to the 지요 ending. It is all right to reduce 지요 to 죠 in spoken Korean, but since an "어" is not used to attach 지요 to the verb stem, the sentence should read as "되죠," not "돼죠."
Sentence number 1, on the other hand, is correct because the polite ending 요 is attached to the verb stem with 어, 아, or 여, which means that 돼요 is an acceptable contraction of 되어요.
Here is a list of more mistakes Koreans make with their language.