Error with format R (with CAPS)

[statquant]

Hello,
I am using the following options let g:jupytext_fmt = 'R:spin' as allowed by jupyter --help
As a matter of fact the following works perfectly

jupytext --set-formats R:spin,ipynb,Rmd --sync test.R
[jupytext] Reading test.R
[jupytext] Updating notebook metadata with '{"jupytext": {"formats": "R:spin,ipynb,Rmd"}}'
[jupytext] Updating 'test.ipynb'
[jupytext] Updating 'test.Rmd'
[jupytext] Updating 'test.R'

But when I try to vim test.ipynb, when I save the file the conversion fails because you jupytext.vim try to run jupytext --to=R:spin --output='/home/statquant/CodeProjects/jupyter/workflow_4/test.r' '/home/statquant/CodeProjects/jupyter/workflow_4/test.ipynb' if it was .R all would be fine