DIAGNOSIS A little moisture or a few droplets during initial heating can happen, but a steady stream or drip from the lid seam is not normal. It means the seal isn't made, usually because the gasket isn't seated or the lid isn't locked down evenly.
FIX Let it depressurize and cool slightly, then unlock. Check the silicone sealing gasket thoroughly. Make sure it's not pinched, twisted, or has a section popped out of its groove. Clean the groove and the gasket. Also, inspect the lid and base rim for any food particles or nicks. When re-closing, ensure the lid handle is directly aligned over the base handle before pushing the lock down. This ensures even pressure on the gasket.
IF THAT DIDN'T WORK The leak might be coming from the vent pipe (the short tube the regulator sits on) if the pipe itself is loose. With the canner cool, check if the vent pipe screws into the lid tightly. If it's loose, you can gently tighten it with pliers, but be careful not to crush or cross-thread the aluminum.
HEADS UP If water is actively forcing its way out, don't continue trying to bring it to pressure. A failed seal means it won't build pressure correctly, making canning unsafe. Always start with a couple inches of hot water in the bottom, but ensure it's not overfilled—too much water can boil over and exacerbate leakage issues.