You must have found it by now because this thread is already marked solved, but for the record in case there's anyone else out there who still can't figure it out...
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All you've got to do is make sure it is for the right post. ie. you need to click the button on the corresponding post with the actual answer as opposed to just any post inside the thread
In this instance, the correct post has already been marked as the answer so nothing else needs to be done.
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