The lid for the ScoopFree machine can be a little complicated to install if you don’t know the trick. It’s designed to “lock” into the machine using the little pegs on either side, which aren’t actually round, but have one flat side.
When reattaching the lid to the machine, hold the lid in a vertical position as shown in the diagram, then slide the pegs into place, ensuring they go all the way in. Then let the lid rotate down into place. The pegs should then be fully engaged in the machine.
If the pegs aren’t fully engaged in the lid it can interfere with the rake, and also fall out of that end of the machine.