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Please correct the following lines:
Jane: Where are you? I'm waiting for you. When you check these messages make sure you reply me back.
John: I didn't go offline. You failed to consider the possibility of power outage. (I means John didn't go offline intentionally; power outage made him go offline)
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Jackson6612Please correct the following lines:
Jane: Where are you? I'm waiting for you. When you check these messages make sure you [reply] (or) [message me back].
John: I didn't go offline. You failed to consider the possibility of a power outage. (I means John didn't go offline intentionally; power outage made him go offline)

You can just say "reply", you don't have to add "back" to it.
Comments  
Thank you, CP.