What are preview and live?

Every new sync starts in preview. It runs exactly like a live sync but writes nothing. Its page lists every variant it would change, with the quantity now and the quantity it would set.

When it looks right, Switch live. From then on your stock follows the supplier. You can go Back to preview at any time; quantities already written stay as they are. Both buttons are on the app's Syncs page and on the sync's page in the workspace.