How do you send a direct message to a user in Slack, using their unique "Member ID". Slack seems to only accept a Slack handle as an acceptable username.
I'm new to Slack and thanks in advance for the help (please let me know if this needs to be moved, etc.).
Assuming you meant user ID when you said "member ID", you can use that as channel parameter in chat.postMessage to send a direct message to that user.
Example for user with User ID U12345678:
curl -X POST "https://slack.com/api/chat.postMessage" -H "accept: application/json" -d token=TOKEN -d channel=U12345678 - d text=Hello
