Passenger Airbag OFF + Seatbelt flashing

[jcs]

Hey there,

I just bought a used 2010 Yaris which was inspected at a local garage and everything was A1 with no DTC showing up.
Couple days later, the airbag light started appearing on the main dashboard, on the passenger side the seat belt light started flashing with the words AIRBAG OFF also litting up.

All this with or without a person sitting on the passenger seat. Even with the passenger seatbelt attached, the same lights are on.
I used a cheap OBD2 bluetooth adapter and found the code DTC B1650 - Occupant Classification System Malfunction.
Using the jumper trick in the OBD2 interface, I got the code 32, confirming the same issue.
I also tried to clear the code using the instructions on the same post, but it comes back when turning on the engine.

I understand that it is the related with the weight sensor under the passenger seat. Either some wires disconnected or the whole sensor that would need calibration / replacement.
Since the issue started appearing randomly after starting up the car, I don't really know where to check.
I checked the front connectors under the passenger seat after disconnecting the battery for 10minutes to check for corrosion but everything is very clean.

Is there an easy way to check if the sensor needs replacement?
Thanks for your help!