The Robo C2 print bed surface is a sheet of black painters tape. Make sure to clean it with rubbing alcohol to ensure your print sticks to its surface.
After 15 or 20 prints, you may need to replace this sheet if you see that your prints are not sticking to it. Ensure that the print sheet is laid completely flat on the build platform, and that it is flush and level across the surface.
When you run out of print surfaces, you can order more at www.robo3d.com.
When removing and replacing the entire print bed, double check that its magnets align with the magnets on the platform to ensure it is seated correctly. Build platforms that aren’t seated correctly will result in failed prints.