Why Instagram periodically denies logging in via OAuth?

I have my application running using Instagram API that has passed the review and received permission to access "public content". For some time the application had problems: authentication (server-side) I get a code which you can later get the access token. Further, as the instructions I make a request to /oauth/access_token and pass in the parameters:
client_id=MyClientId
client_secret=MyClientSecret
grant_type=authorization_code
redirect_uri=MyRedirectURL
code=Polojeniyem

In response to this request I have to get Instagram access token, but in some cases I get a 400 Bad Request. And the reason for the failure to find does not work, I am to her, and after dinner normally enter (the query will be exactly the same). Some of our clients (users) work fine, and at the same time, another part can not pass the authentication. It is sometimes possible to log in if for example to change the Internet provider or the user (and preferably both). The bad thing is that this problem is not predictable, and commercial use under a big question.

Tried a bunch of different advice from stackoverflow, nothing helps. Support Instagram silent, sent them a few queries.
The most plausible theory at this time Instagram some reason bans user and to bundle Username+IP Address+of Epilogue. But neither the cause of the ban, nor the fact of its installation does not know.
What are the options you encounter this error? Or can someone tell me how to get through to support Instagram?
July 8th 19 at 11:45
1 answer
July 8th 19 at 11:47
Understood, Content-Type had to be changed in the POST request.

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