Key Acq Fee in refers to the amount that may have been paid on the date defined in as a fee that represents the value of the acquired asset plus any additional broker expenses.
This amount is denominated in the currency defined in
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 positive if the acquired asset has a positive value at the time of its acquisition
For example, if the acquired asset is a long position on an equity option that has a value - i.e. NPV - of 100 USD when it is acquired, 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.