The system is locking because the water tank hasn't been removed to discard the RO reject water. It's a safety feature.
Lift the water tank and pour out all the leftover water. This is contaminated reject water, not unused water. Refill the tank with fresh tap water to the MAX line. Place it back on the base. The system should restart.
If that didn't work, check the small round magnet at the bottom of the tank. If it's missing, you need a spare part replacement from Bluevua.
You must discard the RO reject water after every filtration cycle. Reusing it causes contaminant buildup and damages the machine.