I think the main problem with this post is that you didn't explain how it's not working for you. You asked how do I share posts to Facebook news feed, I have tried for days. So in what way is it not working for you? Some more detail around this would've helped other users work out what you could be doing wrong and I see now the thread has become requests for your C3 file anyway.
Looks like Ashley's comments are implying that although possible to share to the news feed using IG according to SDK documentation, maybe it isn't possible in Construct 3 plugin and you can only share to the messenger part. OP you will have used this more than me, maybe you can explain what you tried and what is and is not being shared when you use the share part of the plugin.
As in previous post, i have even tried a empty project with just IG , as i said, as of the title of this thread it has not recieved ANY whatsoever relative good responses , so don't even get me started on if i wrote this wrong or not. the title says " How do i prompt wall post instant games?" , do you see anyone even posting something other than facebook SDK's and IG and how they dont work together? Thought so.
So , in conclusion, AGAIN, the problem my friends is that i have IG, all setup, everything is working, ads are working, BUT
when i use the "on click button" if user logged in "share" , nothing happens, in the console, nothing happens, but if i for example extract my whole project and upload to facebook, the audience network works and the IG plugin calls the ads without any issues, the OOONLY thing not showing up, is the actual PROMPT screen that is "share,invite" etc...
That is why i have asked for an example, how would you proceed if you want to share a score on the users board?
I would accept messenger, just weird if c3 has the option if it aint working. but messenger would be great, but now window is popping up.