If you've ended up here, then you're trying to resolve a Stuck Sync that is caused by saving something larger than your remaining free storage space.

DO NOT

Delete your Resonite data/database or cache files. Doing this will likely make you lose your un-synced items, and can cause other side effects
Try to save and sync any more items/worlds. Doing this will add to your sync queue and if your items/worlds are not syncing properly.
Click "Exit & Save Homes". Doing this will also add to your sync queue.
Send any objects or voice messages through the Contacts tab. Doing this will also add to your sync queue and will not send until any syncing issues are fixed.
Change any settings. Doing this will also add to your sync queue and will not save properly until any syncing issues are fixed.
Reinstall Resonite. Doing this does not help syncing issues, as these are stored in a separate location.

Error Explanation

This is caused by an item/world that you are trying to save that is too large for the rest of your storage space, and therefore it cannot be stored.

This can occur, even if your storage indicator says you have storage left.

Please follow this guide on what to do when your storage is full.