Is the awning electric and you're trying to slide something in the "accessory" channel? The power stuff is in the way, you need to rotate the awning tube towards the top (yes you may need a ladder to reach) then the slot will become accessible and you can rotate the tube back down again, fun huh?
Slot in normal position:
Picture taken from the bottom side of the awning.
Slot ready to slide things in. NOTE: You need to over extend the awning for access to this slot (extend fully and keep going until slot is accessable from top)
Picture taken from the top side of the awning