SSRS Standalone install license

For performance reasons we are thinking about moving our SSRS installation to a separate server. Since you can have a standalone installation of SSRS.

Question being, if we install SSRS (standalone) on a new server with X cores. Do we need a separate enterprise license for this server?

Is there a licensing cost for installing standalone SSRS?

Or is the license used from the instance where the ReportServerDB is located ?