Carefully insert your Mac OEM SSD as shown at left, with the golden contact pads below the connector pins facing upward.

The SSD might take a significant amount of force to insert. Make sure you have the orientation correct before you apply any pressure.

When the SSD is fully inserted, you should barely be able to see the golden contact points at the top of the drive, and the notch at the bottom of the drive should be aligned with the hole for the screw in the enclosure.