This permission gives us the ability in the future to offer you the ability to connect with people who are not in your LinkedIn network but who you have found through the TrustRadius site. For example, you might read a review that you believe is particularly good or find another community member with similar technology needs to yours and want to communicate directly or establish a professional connection with that person. This permission also allows us to give you the ability to message your existing connections from within the TrustRadius application.
- The user must be given a choice about whether to send the invitation. The user must opt into the messages being sent rather than opt out.
- The user must be given the opportunity to edit the invitation message text.
- The message must come at or around the time the user invites.
- You must only suggest sending invitations for the purpose of connecting users. Using invitations as a replacement for messaging is inappropriate use of the API. You should use the Messaging API for messages or provide a link back to LinkedIn.com.
Also refer to https://developer.linkedin.com/documents/messaging-between-connections-api which is excerpted below for details on messaging between existing connections:
A message between connections must be associated with a specific user action, not an automated or scheduled event. A user simply navigating through your application is not a significant event. The user must be given a choice about whether to send the message. The user must opt into the messages being sent rather than opt out. The user must be presented with the exact body and subject of the message and have the opportunity to customize both the subject and the body. Pre-prepared messages are allowed only if the user has full control over what is ultimately posted on their behalf. A message between connections must come at or around the time the user took action to send the message. An application must not offer any direct incentive to the user as a reward for issuing a message between connections. An application must not offer any direct incentive to the recipients of a message between connections. Messages posted on LinkedIn must not contain any HTML.