ANot quite sure how to fix this prob. My cakes have been sagging hours after its been finished. By the time the get delivered or shortly after the cake has sagged at the bottom and looks terrible on display. Idl how to fix it. Could it be the weather?

Please tell us about your icing( buttercream, etc. and then we can help you. Thank you Tell us how you put your layers together, etc.

AThank you! It was a chocolate nutella cake, Nutella buttercream filling and chocolate ganach under the fondant. I'm thinking my fondant was to thick but not sure.

Fondant can weigh a cake down. Are you giving time to let your cakes settle before fondanting them? I let mine sit 5 hours which works fine in my hot kitchen. Others place a tile or something on top and let that sit for a certain period.

Sometimes humidity and or/soft fondants can stretch and then make the sides buckle. It's very humid where I live, so I keep an eye on that. I will leave maybe an eight of an inch between the bottom of the fondant and the base so there's some room if it stretches. You may have to watch it and trim more off so you don't get  the buckling. Sometimes I let it sit a couple of hours before attaching any trim so I can cut off more if need be.

Pics would help if you have them.
 

Yes settle the cake with something heavy on it. And I have heard the same about trimming it up a bit higher than the base to allow for settling. Also if you overfill your layers it might cause some of that trouble. I have been experiencing that because I LOVE frosting and just want to put as much of it in the middle as I can, but then the cake gets lumpy or saggy.