Apply a lot of bike grease on the ball bearings and inside of the right (drive side) bottom bracket cup.

Make the ball bearing cages face outward from the center of the spindle. The arms of the cages should wrap around to the cups rather than inside to the spindle face.

Insert the spindle with the excessively greased drive side ball bearings.

If one side of your spindle is longer than the other side, make sure the longest side is facing right (drive side).