Hi,
I have 2 msg.payload A and B and I want to insert after a function like (A+B)/(A-B), but I don't know how to define each msg.payload.
Thank you for your help.
Each function is independent, so function A knows nothing of function B and v.v.
So you can either loom at joining the two flows together (look at the join node) or use a context variable.
Where a flow can read a special variable from another flow. Take a look at the context variable part of the documentation and take a look at the cookbook which contains some examples (cookbook.nodered.org)
