Thank you for your answer. I think this is the only freemium plugin that can more or less manage the automatic publication on Instagram, so congratulations on your work.
I think this problem of “Caption too long” is something that should be fixed, but anyway that’s your decision.
Example:
This morning I published a long post on WP (it’s not so unusual to surpass the amount of 2200 words… it’s a blog system, after all!), let’s call it A, and I got the “Caption too long” message. OK, so I made a copy of the article (a second post exactly cloned, let’s call it B), and I trimmed it to a word amount that seemed to me less than 2200 words. So I published it, with the goal of instantly to delete it. I did so, but I equally got the “Caption too long” message. So I made another cloned article, let’s call it C, more trimmed. I deleted it just after publishing it, and fortunately I didn’t get the “Caption too long” message. Finally I got to have it published on Instagram, but as the article published on WP is A and the one published on Instagram is C, the link that appears in the end of the IG caption isn’t correct, but this is a minor problem.
This is the trick I’ve used, in case it’s useful for another user, but I’ll look through this forum in search of other tricks.