Why it is saying "complete the previous lesson to unlock this one"?

Answer 1

That also happens when you do not press "continue"

Answer 2

As @Tobias and @Sreejith said,

You need to do the lessons in order to continue.

Answer 3

sometimes there is a glitch that makes it so the next lesson didn't unlock so you just need to do that one again.

Answer 4

so that you try to implement the knowledge before going to next lesson

Answer 5

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