I can't replace my Realm with existing worlds (Nintendo Switch)

I purchased realms to for me and my friends to play our existing Minecraft world without having to depend on me to be online to use it. However since purchasing a realm I get an error occur and my world export fails.

This happened to all of the worlds I have on my switch varying from 1mb - 50mb. If this cannot be resolved I would like a full refund on my realm subscription.

 Many Thanks