Hello guys,
We had a chance to API listing that ended up affecting other parts of the Marketplace such as making comments and delivering items/marking the item as sent.
This is now fixed and the limitation will only affect API listing when the seller is creating lots of listings in a certain period of time (spamming). Such a limit can vary, so the only way to avoid that is to create listings at a moderate pace.
If you find any issues and/or have questions, please feel free to comment on this post.