I created small python library to serve and eBay application and work with clients' orders using access tokens. I used this flow https://developer.ebay.com/api-docs/static/oauth-authorization-code-grant.html and my application successfully worked for about a month.
But now every time I try to exchange the user's auth code to access token, I get 400 error from eBay API. The main problem is that the response content is empty so I can't see any kind of explanation of what is going on (see response). As for sandbox, all works well. I didn't change anything after ~40 users successfully authorized through my application.
I'll appreciate any help.