About advertisement posts of your own novel
I think it means you cannot post a duplicate of the same story on the site twice.
Or it means you can only link to your own website (or amazon) once a chapter (not 'author').
For clarification, can you direct us to where you are seeing this?
(Or you can post a support ticket)
You can make a post in the Promotional Section linking to your novel (once per novel created). Because so many (I believe there are over 14,000 novels on here, at the moment) are updated daily - heck, hourly, if people were to continuously update their own Promotional Threads with chapter updates etc, everybody would lose there own's position in the Forum within minutes of posting (much like your novel only shows under the Recent Updates section of the main page for around 30 minutes before enough other stories have been uploaded to knock it off the list).
By only allowing one promotion per novel, perhaps 10-20 threads are added to the Promotional sections per day. This keeps it manageable to check in once every day or two and see what is new that you may have missed due to how fast the Recently Updated section turns over.
Is it the best rule? Debatable - but it does help keep the forum clean, and ensure that if you look in the Promotions thread once a day, you'll actually have a good chance to find what was posted about that day - rather than pages and pages of "new" additions.
However - there are posts dedicated to pointing out "New this month", for example. That is another place to seek listing your novel. There is also the WriTE group, which has a thread of Completed Fictions By Members, and Ongoing Fictions By Members. If you're a member, those would be additional places to see it.
You can also join the Discord, and mention updates to your story there as well, and of course add your novels to your signature.