Instagram returning "Matching code was not found or was already used" when using OAuth

We are experiencing the same issue. It appears that logging out of Instagram, then attempting to use Instagram OAuth through our site after we are logged out of Instagram is a workaround.

We're experiencing the same issue since yesterday (after months of working fine) - have reported it as an issue yesterday via the 'Report Issue' function on https://www.instagram.com/developer/clients/manage/ and I'd encourage you to do the same.

Yet to hear back, but seems likely it's their end having issues rather than something we're doing.

EDIT: It's also working fine for us on our development servers (which use different IPs for interacting with IG's API) but not working on our production server from any of the IPs we have available on the production server.

EDIT2: (July 2016) Just tested and it's mysteriously started working again on our production servers. No reply to the support ticket from Instagram as yet.

EDIT3: (December 2016) And now it's failing again with the same message... Seems like it's Instagram's end again. Nothing much we can do. Frustrating.

Logging in to Instagram, then complete Step 1 from the API Docs (https://api.instagram.com/oauth/authorize/?client_id=CLIENT-ID&redirect_uri=REDIRECT-URI&response_type=code), then follow the redirect and copying the code from the URL, then logging out of my account, then completing Step 3:

curl -F 'client_id=CLIENT_ID' \
-F 'client_secret=CLIENT_SECRET' \
-F 'grant_type=authorization_code' \
-F 'redirect_uri=AUTHORIZATION_REDIRECT_URI' \
-F 'code=CODE' \
https://api.instagram.com/oauth/access_token

That worked for me.