Disp Fee

Key Disp Fee in
Ledger Entry refers to the amount that may have been paid on the date defined in Disp Date as a fee that represents the negative of the value of the disposed asset plus any additional broker expenses.
This amount is denominated in the currency defined in
Disp Ccy
It is also assumed that this amount is paid without delay exactly on the mentioned date.

This is an outgoing amount, which means it must be negative if the disposed asset has a positive value - at least of the brokerage fee is ignored - at the time of its disposal
For example, if the disposed asset is a long position on an equity option that has a value - i.e. NPV - of 100 USD when it is disposed, then the number here must equal -100 + X, where X is the brokerage fee.

The amount defined here can have no impact on the pricing of the referenced tradable, for the simple reason that it is not regarded as part of the contract specs that define the asset's cash flows.
Deriscope nevertheless reports it as part of the reported cash flows and PnL, if applicable.