Bismillah
Salamun Alaykum
Radde madhalim basically is an ‘amanah’, meaning a deposit, in ones hands. According to the Islamic law, the ‘amanah’ has to be returned to its rightful owner or a permission to possess it should be taken. If one is unable to identify the owner of the ‘amanah’ , the possessor of the ‘amanah’, with the permission of his ‘marj’a’, should give the ‘amanah’ as sadqah- alms to the needy, and or give the amount equivalent to it (as charity-alms).
Person wishing to pay ‘Radde madhalim’ should give the exact amount of the ‘amanah ’ and in case of not knowing the exact amount, he should then pay the amount that he believes (has ‘yaqin’) it to be so. In case of a person who is completely unable to tell the amount or approximate it, he should then pay sum of 1/5 of an amount- counted as haram -as alms. This again should be done after obtaining the permission of his respective marj’a.
The purpose of paying ‘rade madhalim’ is to clear a debt that one is holding by possessing a deposit. This is one of the referents of ‘haq-un-nas’
Iltemase Dua