I am assuming by project planned activities you mean costs at activity level - this is what would be recorded in the project forecast, typically. The project cash forecast can be copied from a project forecast, taking into account the spreading from the project forecast + IFS will apply period delay based on the definition against cost elements. 

CONTINUED - By linking a cash plan snapshot (finance) to the project cash forecast - this will take specific items (invoices, subcontract valuation plan etc.) with payment terms applied and spread those automatically in the project cash forecast. The project forecast spreading is only necessary for the “tail” (the difference between the total project budget and items available in the cash plan).

@Ieva Rituma  Thank you!