Two things cause almost every manifest failure: a blocked pop-up, or a single order in an irregular state.
How to fix it:
Allow pop-ups for PDQ - the manifest opens in a new window.
One bad order blocks the whole manifest. Usually it's an order with a duplicate label stuck in a
pendingCancellationstate (from a label being printed, sent back to Assign, then re-labeled). That order needs to be resynced and its label voided - contact support if you can't clear it.Create the manifest for the same day - a manifest can only be created for the current day; you can't back-date a missed one.
💡 Prevention: don't send an order back to Assign once its label is printed - that's what creates the duplicate-label state.