sn_connect send message is not working in the business rule. can run it in background script fine

[b__BenjieB]

            var conversationId = sn_connect.Conversation.get('sys id of the conversation);

            conversationId.sendMessage({

                body: "Please don't leave the chat some agent will take over your conversation",

                field: 'comment'

            });

the error I found is this 

Root cause of JavaScriptException: graphql.GraphQLException
: graphql.GraphQLException: User can not send message: com.glide.cs.domain.UnifiedMessageSender.sendMessage(UnifiedMessageSender.java:818)
com.glide.cs.domain.UnifiedMessageSender.sendMessage(UnifiedMessageSender.java:675)
com.glide.cs.domain.UnifiedConversation.sendMessage(UnifiedConversation.java:138)