I am using
PUT https://api.linkedin.com/v2/eventSubscriptions/(developerApplication:urn:li:developerApplication:{developer application ID},user:urn:li:user:{member ID},entity:urn:li:organization:{organization ID},eventType:ORGANIZATION_SOCIAL_ACTION_NOTIFICATIONS)
Linkedin API with all the parameters intact. Each URN is encoded as urn:li:organization:12345 is encoded to urn%3Ali%3Aorganization%3A12345 but still getting a 403 Response.