No voltage on the battery output usually indicates the BMS has shutdown output to protect the pack from damage from overdischarge. If your wattmeter doesn't indicate you used the full capacity of the pack yet, then that usually means the pack is not well-balanced, or has problematic cells (often itself a cause of imbalance).
If that's the case, plugging it into the charger and letting it cahrge at least overnight, should at least let it re-enable the output, and at least partly rebalance the pack.
It can also be a broken wire inside the battery pack, if you are measuring no output rigth at the pack terminals.
Could be a blown fuse.
It can also be a failed BMS.
I would recommend looking around at the many battery troubleshooting threads, for the lists of things to test, or contact the battery seller for warranty repair.