CloudExport results in a blank file

I'm trying to convert a 2d image to a 3d object that can be digested by 3d slicing software, specifically the algorithm contained here http://archive.bridgesmathart.org/2013/bridges2013-311.pdf

I had to convert the input/output of the routine to the below, however my cloud file just contains the wolfram comment 'created by wolfram' and no actual STL file.

SetDirectory[\$UserDocumentsDirectory];
img=ColorConvert[Import["bone.png"],"Grayscale"]      (* import the image as values in range 0..1 *)
height = 2.0;   (* height of cylinder.  Units are set in the 3D printer *)
alpha = 0.1;   (* max relief depth, as fraction of height, typically around 0.1, or -0.1 for inverting *)
{n,m} = ImageDimensions[img];
rMid=n * height/(2 Pi m) ;     (* scale so pixels are square at mid-depth*)
r=Map[rMid-alpha height (#-0.5)&,ImageData[img],{2}];   (* convert to table of radii *)
xyz=Table[{r[[j,i]]Sin[2 Pi i/n],r[[j,i]]Cos[2 Pi i/n],(1-j/m) height},{i,1,n},{j,1,m}];   (* convert to Cartesian *)
(* the cylinder consists of three parts: the curved surface with the image and two circular caps: *)
surface=Table[{xyz[[i,j]],xyz[[Mod[i+1,n,1],j]],xyz[[Mod[i+1,n,1],j+1]],xyz[[i,j+1]]},{i,1,n},{j,1,m-1}];
bottom=Table[{{0,0,0},xyz[[i,m]],xyz[[Mod[i+1,n,1],m]]},{i,1,n}];
top=Table[{{0,0,(1-1/m)height},xyz[[Mod[i+1,n,1],1]],xyz[[i,1]]},{i,1,n}];
g=Graphics3D[{EdgeForm[],Map[Polygon,Join[surface,top,bottom]]}] ;
CloudExport[g,"stl","export.stl"];

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