How a publication is counted
A post is the draft. A publication is the billable unit. They are not the same number.
The rule
Count the target accounts on each network, then take the largest of those counts. Instagram, TikTok and YouTube with one account each is 1. Three TikTok accounts is 3. Two Instagram accounts and three TikTok accounts is 3.
Trial
The free 15 publications belong to the user for the calendar month. A new organization does not reset them. A paid organization does not spend the trial counter.
What does not count
A draft does not spend a publication. Cancelling a scheduled post releases the reservation. A text post and an image post use the same rule: the count is targets, not the kind of file.