How to count the number of messages The number of messages is counted by the number of people to whom the message was sent. For example, even if you send a push message with four message objects specified in a single request to a chat room containing five people, the number of messages counted is five. The number of message objects specified in a single request doesn't affect the number of messages sent.
Also, if you send a message to a user ID that has blocked the LINE Official Account, a user ID that doesn't exist, or to any other users that won't actually receive your message, it won't be counted as one message.
@ksyt Thank you for your prompt and accurate response.