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は駄目ですよ

must not

→ は
phrase Uncommon #14,845
must not Used after a verb in the て-form to say that doing something is not allowed or is unacceptable. 駄目 means “no good.”
JA: 嘘をついては駄目ですよ。
EN: You mustn't lie.

こんなところを一人でぶらついていては駄目ですよ。

You shouldn't be wandering around a place like this by yourself.

外出は駄目ですよ。

You must not go out.

太っては駄目ですよ。

You mustn't gain weight.

それは駄目ですよ。

That’s not allowed.