Noob FBA question

Hi, I’m new to FBA and I did a quick profit calculation about buying the items and selling it to Amazon warehouse, but it seems something wrong, I just don’t know what it is? Here is the math:

Investment:

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100 units of X = $600 ($6 each)

shipping = $100

Amazon advertising = $1000

Total investment = $1700

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Selling on Amazon:

price per unit = $27

selling 80 units (for example) = $2160

Amazon total fees 33% (i read somewhere on Reddit, that I should always cut almost 33% of Amazon FBA taxes from the profit) 33% of 2160 = $712

profit = $712

investing ($1700) – profit ($712) = -$988

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final profit = -$988

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why I’m losing money? What exactly is wrong

Thank you guys, and sorry for my English.

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