How to feed the filament through the material shortage sensor? !Sensor , there is something that prevents the filament from going forward. I don't see any switch on the outside of the sensor, and I applied a reasonable amount of force on the filament. Can you tell me how to troubleshoot this ?

I've designed similar sensor casings, sometimes the filament catches a ridge/ledge or part of the cavity, even when it is chamfered or rounded. The arm of the limit switch pushes the filament up, away from the filament straight path.

Have you tried cutting the filament under a very sharp angle, that may work.