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

The SSD and enclosure are both keyed, so the SSD can only be installed one way.

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, the notch at the bottom of the drive should be aligned with the hole for the screw in the enclosure.