Hello together,
Reefmaster is currently (V2) not supporting the export of 3D Files that are suitable for 3D Printing (.STL, .OBJ)
Here is a workaround if have tried and it works very well:
1. Create your Map
2. Set the Layer "Flat Raster" to a Grayscale palette
3. Switch off all other layers
4. go to "Export" (PNG Image) an set Background Colour to "Transparent"
5. Convert the .png File to .STL e.g. with this Tool:
imagetostl.com/de/konvertieren/datei/bmp/in/stl
6. Download the file an print it
7. Be happy