sylvio,
the reason for this happening sylvio is because by the time your debt reaches collections, your payment options have gone down to none.
collection agencies are hired by clients (creditors) to collect their bad debts. they want the agencies to collect the debt in full and they want a financial done for monthly payers. they want to know that the "monthly payer" can't afford more then that monthly payment thus the financial.
when a debt goes delinquent into collections, time to make monthly payments are done. that's just the way it is. it's payment due in full today.
I suggest you do the financial then perhaps they can work with you with the OK from the client and have you make monthly payments.