In-app purchase - Apple ID couldn't be found

I'm unable to make In-app purchase (for lat day or two) - after asking me to input my credentials - system shows me standard dialog with "An unexpected error occurs during signing in" title and "The apple id you entered couldn't be found or your password is incorrect" body.

I'm 100% sure login and password are correct - I used them to login on this site for example.

Also I've tried several applications with in app purchases and asked friend of mine to try it on his Mac - every time we get the same error.

How could it be fixed or this is temporary problem on Apple side at the moment?