Thanks, I already use them, very handy!
After some research I found another service that is very easy to use and (as of now) free of charge: https://mockup.io/about/ It's perfect for my needs, just export slices from Affinity, upload them, create link zones and a fixed header and you're ready to go.
EDIT1: And just reading into the topic a little bit more, here is a list of other, similar tools that could help: Briefs, InVision, Notism, Flinto, Fluid, Mockup.io, Prott, POP, Marvel, Balsamiq, Red Pen and Keynotopia.
EDIT2: In the end I went for Invision, Mockup.io is abandoned and sometimes works and sometimes does not work (unfortunately). What I would love to see now is a workflow form Affinity Designer to Invision, as it's already possible with Photoshop.