Any world that has been previously created while playing Minecraft on the Nintendo Switch gives me this error when I try to export it to Realms:

Level export failed 

I've tried multiple different worlds created on Switch. They all fail. I've tried with worlds created on Microsoft Windows 10. Those export to Realms just fine.

I paid for and subscribed to Realms specifically so I could export a world created on Switch. If this issued cannot be resolved or Switch created world are simply incompatible (as it seems) I will require a full refund.