Once you send a direct or private message to someone else on Meetup, you can ensure that the message was received and read by relying on the double checkmarks displayed on your message. Whenever they appear, it's a sign that your message was delivered and read!
If the possibility of sending DMs is greyed out or not available, it could be due to several reasons. You can learn about them by reading our article Why am I unable to send messages to others?