AirDropping a swatch from the mac to the iPad doesn't seem to work (you can save it on your iPad, but no reaction otherwise).
So as a workaround:
- start affinity on macOS
- go to your swatches and export
- open a new empty document
- go to your swatches, import as document palette and select the swatch you exported.
- save your swatches.afphoto image
- open affinity on your iPad (main screen, not working on an image)
- airdrop your swatches.afphoto image from the mac to the iPad
- Now you can open your swatches...
Not great, but at least I didn't have to manually set hundred or so colors.