ARCORE - How to get projection of a point on to another point in a specific direction?

I'm trying to project a point on to another point in a specific direction.

As shown in the image, I have two points P1 and P2. I want to project P2 on to P3, in an orthogonal direction of P1 and P2, to create P4 on the same plane

I have tried below methods(Pseudo code) but didn't work

1) Vector3.Project(P2.transform.position, P3.transform.position)

2) Created a plane GameObject at P3 and tried using Vector3.ProjectOnPlane(P2,P3.getComponent.normal)

Could you please help me in projecting P2 on to P3 to create P4.

Thanks in advance!