If one (1) message is published to 100 active subscribers (all subscribers receive the message), it is counted as one (1) published message and 100 subscribed messages for a grand total of 101 messages.
Other APIs that increment the message count are:
- history - one for each message fetched
- missed message catchup - one for each message fetched
- presence - one for each message sent (join, leave, timeout, state-change) and received (same scenario as publish/subscribe)
- mobile push notification - each push notification that is delivered is counted but unsuccessful attempts to deliver a push message are not counted (mobile push messages are currently not part of the total billed monthly messages).
- web hook events - each is counted as a published message but not as a subscribed (received) message.