It's supposed to spin, but likely rusted, fused to the tube inside the fitting. You can try Kroil or PB blaster and shoot it in the backside of the fitting between it and the tube, and soak it good giving it time to work it's way in. Gently see if it will free up.

Inspect well before starting to work it in the event that there is a back weld as Sugar Bear indicated. These types of flares are usually meant to spin just like on a brake caliper.

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