Do you have an instruction guide for the Mamas and Papas Luna? I can't figure out how you should snap on the lower basket.
Here is a Mamas&Papas Luna stroller manual so feel free to check that out. I don't believe they go into details so I personally would google various Luna stroller images and try to get to know how it works from those (+ stroller videos). Also, I recommend always taking pictures or recording videos of how you remove fabrics and parts of your stroller so you can get back to it when putting the parts back on-