There are two category calendars, one for topic calendars (calendar categories) and one for Event calendars (events calendar categories).
Those instructions are for displaying a topic calendar on top of one or more of your categories. Post_ids are not that user-friendly to find, but you can pick it out of the json of your calendar topic. Ideally, we’d have a much easier way to find that out.
The Event category calendar is the one that gets populated with the ‘create event’ style ones from the first posts.
Not understanding why two calendars would be needed, or why they hold the same name.
I probably never bumped into a “topic calendar”. From what I understand, the “topic calendar” would allow a single topic to hold a calendar in its first post (so, potentially publishable as a page) that can be populated from replying to this topic with an… entry?
I think using the topic_id/post_number shortcut may be a good start. It’s easy to find since it’s part of the URL. But it may change if the post is moved. So one way to handle this would be to use 123/45, and convert that to the actual postId automatically. So when the post is moved, the other conversion is doable (e.g., postId=444 would become 222/67 once moved from 123/45 to topic 222.) I think it requires an additional SQL table to keep track of this relation, but it would be so much easier for users to understand. And also would enable referencing posts like this…
“Please refer to post:134/33…” and that would automatically create a link to that post.