じゃなかった ｖｓ． ではなかった

[testfugu]

Sometimes, when I am reviewing the casual past negative copula, Bunpro accepts じゃなかった, but shows ではなかった as a more correct answer. What is the difference between the two?

[seanblue]

じゃ is a contraction of では, so it’s more casual.

[mrnoone]

Like @seanblue says

You can also hear/see ではありません, the most polite version.