Looks like a piece of he bottom seal is missing.
On my slide there is a "wiper" type seal that covers this gap, attached to the frame and sealing off the bottom of the slide. End seals are turned in at the bottom so when the slide is in they plug this area as well.
Tell FR to make yours just like all the others that they've sold and make it not leak too.
"A wise man can change his mind. A fool never will."
"Sometimes you're the dog, sometimes you're the tree"
2018 Flagstaff Micro Lite 25BDS
2004 Nissan Titan