The installed springs hold the folding carrier (in the best case) rattle-free in an upright position.
Folded down, it stands (depending on the model) possibly over the back (possibly bad when stored in garage or bad when maneuvering).
If you want to have him permanently folded down:
1. for the original folding carrier there is a small (overpriced) plastic clamp (number 623576), is unfortunately often stolen / lost
https://www.sip-scootershop.com/en/product/clip-piaggio-luggage-carrier-rear_PI623576
2. cable ties (There are also reusable cable ties) OR Double sided velcro
3. on some models, the springs can be inserted upside down, then the flap is permanently pressed down.
Imho this belongs upright and is only folded down for use