It is, but in a slightly convoluted way (specifically, it’s defined here).
The problem seems to be accessing some data via the REST interface… Is there anything earlier in the server logs? Alternatively, in your browser network tab do you see a failed request for either the /concept or /obs endpoints?
Yes! that is working…the additional quotes seem to be unnecessary after all (and in fact are the trouble makers).
With the additional quotes removed and the Widget config changed to this, a nice multi-variable graph is produced showing Weight, Height & BMI:
However, if you observe the value of the BMI…it is 10x times more than the expected. But, that is a different issue altogether…and we will have to look through the function being used for this calculation and other pieces of codes.