(08/24/21)

-난 너의 메시지를 오해했어. I misunderstood your message. ✔​

-그는 레몬주스와 꿀을 섞었다. He mixed lemon juice and honey. 

*He combined lemon juice and honey.  

~> This sentence is okay. This is another way of saying it.​

-그들은 그들의 약혼에 대해서 발표했다. They represented about their premarriage.  

*They announced about their engagement.

~> Your sentence has a correct grammatical structure, but this has the correct usage/expression.​​