Hi, @martinratinaud, and welcome to our Netlify community site. 
The rule use used should have worked from what I can see. In order to troubleshoot why is isn’t working, I’ll need the actual URL at Netlify which isn’t redirecting or proxying correctly.
Or, if you prefer, you can send us the x-nf-request-id header for the request which didn’t proxy correctly.
Would you please send us either set of information above and we’ll be happy to research this further?