Simlabs keyboard tray install issue

[Britkart]

Have mounted the sim labs keyboard tray but it falls down with weight put on it. Not sure what could be wrong and what are the 4 metal pieces in the supplied bag?
Any help would be appreciated

 

[LeeHetherington]

You use two of the metal pieces to fit in the holes of hinge and then they fit into track to resist twisting.

 

[Britkart]

You use two of the metal pieces to fit in the holes of hinge and then they fit into track to resist twisting.

Thanks will give that a go!