DIAGNOSIS: The floating valve pin is likely stuck in the up position from a previous cook, tricking the lid sensor into thinking the pot is already pressurized. This prevents the lid from turning fully into the locked position.
FIX: Manually push the stainless steel float valve down until it clicks into its seated, down position. You'll hear/feel a click. Now the lid should turn fully and lock.
IF THAT DIDN'T WORK: Check that the silicone sealing ring is seated properly in its groove around the underside of the lid. A misaligned or pinched ring creates an uneven surface that can block the locking mechanism.
HEADS UP: Never force the lid to turn. If it won't lock with gentle pressure, the issue is with the valve or seal, not the handle. Forcing it can damage the locking pins.