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 it can cause other side effects.
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.