I found this playground, which seems similar to your approach, one difference being in line 20, not sure if changing your line from “data:64encode,…” to “data:64,…” also would make it work as it does in the playground example :
thnks for reply : when i tried the same 64Encoded string in that example it work perfectly , when i used my stl file (64Encode) it fail , i tried many files with same result , so i suspected that the engine not support stl 64Encode .