What are the contradictions between the classical law of addition of speeds and data on the speed of light?

According to the classical law of addition of velocities, the speed of a body relative to a stationary frame of reference is equal to the sum of the speed of a body in a moving frame of reference and the speed of a moving frame of reference relative to a stationary one. However, it has been experimentally proven that the speed of light does not depend on the speed of the frame of reference, but is a constant value, i.e. invariant.

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