Thanks for the solution, I have now updated to version 1.0.4, downloaded and installed again.
In the SetNPCIcon command, specify:
mapId: The map ID where the NPC is located (0 will use the current map)
npcId: The ID of the NPC you want to set the balloon for
The other parameters are as you want
For ClearNPCBalloon, specify mapId and npcId as well.