How to grant Userpoints after adding a comment once?
I solved my problem with the Flags module: I created the flags called 'Commented on this node' &amp; 'First reaction'* and rule called 'Commented on a node'. These are my rule's settings:

EVENTS: After saving a new comment

CONDITIONS:


Content is of type Parameter: Content: [comment:node], Content types:
Article
NOT Node is flagged Parameter: Flag: Commented on this node, node:
[comment:node], User on whose behalf to check: [comment:author]


ACTIONS:


Grant points to a user Parameter: User: [comment:author],
Points: 2, Points category: Reaction, Entity: [comment:node],
Description: New reaction, Operation: Add,
Display: false, Moderate: Automatically approved
Flag a Node Parameter: Flag: Commented on a node, Node:
[comment:node], User on whose behalf to flag: [comment:author], Skip
permission check: false
Flag a Comment: Parameter: Flag: First reaction, Comment: [comment],
User on whose behalf to flag: [comment:author], Skip permission
check: false


So, every time a user adds a comment to a certain node for the first time, the node is flagged as 'Commented on a node', the reaction is flagged as 'First reaction' and the user who added the comment is rewarded 2 points.

**I use the 'First comment' flag in a related question.*