Repayment Negotiation

I pay a fixed monthly to a collection agency {two consolidated debt accounts} and also pay a creditor directly monthly so that my monthly discretionary spending is less than $100. My total yearly gross will soon be reduced by $ 2,000 due to reduced total work hours. I have modified a repayment letter template yet not sent yet; a repayment letter asking for reduced monthly payment negotiation. Ideas about what to admit and not to admit in it before I send this letter ?