I am seeing this error from my live server using the Instagram API.
{
"Error":true,
"message":"Matching code was not found or was already used."
}
I have read a few suggestion on here to clear cache but that isn't fixing the issue. I am also unable to submit a support ticket directly on the Instagram site as I am receiving an error message while attempting to submit a ticket.
There are a bunch of developers complaining about the same issue at https://news.ycombinator.com/item?id=13178789. I don't think unchecking "Disable implicit OAuth" fixes the issue as I have already tried that and it didn't work.
The best thing you can do is to submit a report to instagram using your client id to put some pressure on their side to fix this issue.