Your messages with matches are always private and never visible to your friends. The first time you message a match, Ship notifies all friends who have the 'When I DM a match' permission granted of this special moment through the feed, but your message itself will always stay private.
To manage which feed updates are visible to your friends:
- Tap on your profile avatar in the top left.
- Tap on 'Permissions'.
- Under 'What can friends see' select the 'When I DM a match' menu to select which friends will see this in their Activity feed.