The Watson Assistant node on node red accepts as input a payload with a String, however in my chatbot, I had configured a variable "$user" to receive the username, but I am not able to assign a name to this variable.
Can anyone help me with this?
I am guessing that your dialog is outputting Hello $user.
For this to work $user needs to be set in the context. This is normally done by your dialog when it has determined the name. When responding your dialog should check if the context $user is set.
See the service documentation - https://cloud.ibm.com/docs/assistant?topic=assistant-dialog-runtime-context