Is zakat obligatory on money given to a merchant for investment if the monthly return barely covers expenses and obligations, with nothing left over at the end of the month?

Zakat (definition) is obligatory on paper currency if it reaches its nisab (definition). If it is invested in trade, its zakat becomes obligatory every time a hawl (lunar year) passes since the ownership of the original capital. The goods should be valued at their selling price at the end of the hawl, and liquidity and collectible debts should be added to this value. Then, 2.5% of the total amount is to be given out. The capital and profit are subject to zakat upon the completion of the hawl.