The ornamental design for a magnetic fastener with fixing unit, as shown and described.
FIG. 1 is a bottom isometric view of the male fastener and the female fastener of a magnetic fastener with fixing unit in their separated or detached position with female fastener member overlying the male fastener member.
FIG. 2 is an isometric view of the male fastener and the female fastener of the magnetic fastener with fixing unit of FIG. 1 in their attached or fastened position;
FIG. 3 is a top isometric view of the male fastener and the female fastener of a magnetic fastener with fixing unit in their separated or detached position with female member overlying the male fastener member; and,
FIG. 4 is a top isometric view of the male fastener and the female fastener of the magnetic fastener with fixing unit of FIG. 3 in their attached or fastened position.