Model not a solid object issue

[Mo_Dev]

Sometimes when I upload a Blender model to Roblox I end up with something that is not a solid object like this,

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I was wondering how I would fix that.

[1Joeb (joeberson)]

Having an issue with my Mesh - Please help!

Check your surface normals: https://codeyarns.com/2013/10/22/how-to-display-normals-in-blender/ To flip normals: https://blender.stackexchange.com/questions/29132/how-do-i-flip-normals-on-this-model

[fourpapa1]

Try this: Why are faces being deleted when importing a mesh? - #2 by RegularRival