My guess is that either the features collection or the bodies are not in the same context. I can't tell from your code because the code that shows where you got those are not displayed. I tried a simple case where I deliberately had bodies in two different components and provided both bodies in the context of the component that owned them. In that case, I got the clearer error shown below, so yours is something different. When I provide the correct context, the move was successful.
Failed:
Traceback (most recent call last):
File "C:/Users/t_ekinb/AppData/Roaming/Autodesk/Autodesk Fusion 360/API/Scripts/Samples/Samples.py", line 548, in createMove
move = moves.add(input)
File "C:\Users/t_ekinb/AppData/Local/Autodesk/webdeploy/develop/6154ed41f984a6d55387f8e7e8a12643fced376b/Api/Python/packages\adsk\fusion.py", line 27058, in add
return _fusion.MoveFeatures_add(self, input)
RuntimeError: 3 : object is not in the assembly context of this component
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Brian EkinsInventor and Fusion 360 API Expert
Website/Blog:
https://EkinsSolutions.com