The term "Royalty Free Music" is often misunderstood and equated to eg.  "GEMA-free". Royalty Free only means that the rights to use the music have been clarified in advance and that the customer does not incur any further follow-up costs on the part of the licensor. It does not automatically mean that the music is GEMA-free. The license costs for royalty free music are often comparatively cheap and the music can be used in several films. This is possible because rights holders receive additional income from the collecting society each time they use the music. Assuming that you used royalty-free music, the surprise is great when you suddenly receive an invoice from GEMA. Notes in the license terms of such providers, such as "Please note that our licenses do not include public performance rights" mean that the music is subject to  eg. GEMA.