Are management fees forbidden for the property manager if he receives them after the owner has paid the mortgage installments, knowing that the manager does not pay or contractually participate in the mortgage in any way?

It is permissible to work in property management and leasing for a percentage of the rent or a fixed amount. This is a permissible agency and brokerage contract, and there is no objection to the fee being a percentage of the rent. It is stipulated that this work should not be an aid to something forbidden, such as brokering the lease of a property to a usurious bank or for a prohibited purpose. As for purchasing homes with a mortgage, it is explicit, forbidden usury. However, whoever buys with it legally owns the property, while incurring the sin of usury, and must repent. It is permissible for him to benefit from the house. Consequently, there is no objection to brokering the lease of a property that was purchased with a mortgage, unless the broker participated in the usurious loan or aided in it.