What’s important regarding the 3 points P1, P2 and P3 is that the P1P2 vector gives the “forward” direction, and P1P3 the “left” direction. They should be orthogonal, and only a single value among the three x/y/z axis should be non null in P1P2 and P1P3. Also, P1/P2/P3 should be in the local space of the mesh.
Here’s a setup that works in your case: