Error when replacing realm from Switch

Hi,

I am a Realms plus subscriber and I am trying to replace my realm with a world I created on the Nintendo switch. Whenever I try to do the transfer I get an error msg stating: "we couldn't pack your world file for upload. maybe your hard drive is full"

I have a lot of space of my switch so not sure that is the issue - can you help? What do I need to do to resolve?

Thanks