Flip cover not turning off display - hall sensor

Hi, I’ve just purchased a flip cover, but it doesn’t turn off display when closed.
It seems that this is triggered by the hall sensor (not the proximity sensor) when it records a magnetic field.
Is it correct?

Evidently this cover doesn’t have a magnetic tape on it.
Did someone knows where the sensor is located?
Where can I find a magnetic tape?

Meizu m2

I have strong magnet when i place it underneath front camera screen goes black

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