Reconsideration letter

Hi is a reconsideration letter just simply you say you do not agree with the decision and are wanting them to reconsider or do you write something yourself like a novel lol just trying to see what should be done when sending off the letter we were denied cause it says was not severe or prolonged if anyone has any guidance in how to proceed this would be forever helpful
Thank you

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I haven’t done it.
I suspect you would provide more medical documentation proving your condition is severe and prolonged.
Don’t get discouraged, a lot of people get denied (Service Canada might not even read the application).