3d print Mesh error

Job ID: 37884644

Budget: £5 – £10 GBP

Hello i have downloaded a 3d model from the normal online car sites. I have added some extra extrusions to the model and want to get it printed.
I think it’s because of the surfaces and model not being combined?

My 3D printer has said there are some mesh errors and sent the following screenshot over.

Job is to fix the STL so it can be printed