I have a few Withings devices (pulse, scale, BP monitor, etc), so your theory makes good sense. Kudos, by the way on this proof of concept - I like it and this will be one of my first Pi / Magic Mirror / module customizations, so I appreciate any insight you have.
The errors appear at MM_Withings.js:208, which I believe is the line that writes the error to the log.
Per the console, I do receive weight (poids=90.67;) and date (date=1481195497) information, but then see the following:
status=0
error TypeError: Cannot read property ‘date’ of undefined
error TypeError: Cannot read property ‘body’ of undefined
data=undefined
data is null
@frog I’m getting the same results as you. I suspect the MM_Withings.js script needs to be tweaked a bit. I manually tested all the variables used in the config.js file, confirming that the API is setup correctly and returning data. My guess is that the output string of the MM_Withings.js script is different than what I’m testing.