Split meshy ai model are empty

Hi everyone,
I’m using Meshy AI, and I think it’s great for single-color 3D printing.
The issue is that I’d like to split my 3D models into different parts so I can print them in multiple colors without spending hours or days on a single print.

I’ve tried splitting the models both in Blender and directly in Meshy AI, but the problem is that the models are hollow inside. When I try to make them solid and then print the parts separately, they don’t fit together perfectly once printed.

Has anyone found a good workflow or solution for this?
Thanks in advance!