If you sign up with Facebook's Instant Articles program, you will likely meet various obstacles during the process. This is especially true if you are not that familiar with programming languages and other coding-related issues. I signed up with Instant Articles a few days ago and it was all going well until I came to the "Submit for Review" section of the initial setup. A "missing logo" error message and notification keeps appearing which prevented me from submitting the five articles I just created.
Basically, the error message is as follows: "Missing logo. All articles must include a logo, which you can upload in the Style Editor." Needless to say, I went to the Style Editor section and created a new style. I uploaded a logo which is a picture that I've used in my website for several years. However, after uploading and saving the logo in the new style I just created, the "missing logo" error still appears on my configuration page.
Obviously, creating a new style and uploading a logo is merely the first step in fixing the error. What you need to do is go back to the "default" style and upload the same logo. Save it, wait for a few moments, refresh, and check if the error message has disappeared. This worked for me so I hope that it will work for you as well.
Once the "missing logo" error notification on Instant Articles has disappeared, you can now submit the initial articles you created for review. You will receive the following notification after submitting your articles: "Your review is currently pending. Article reviews are usually completed within 1-3 business days."
Always keep in mind that you won't be able to start publishing Instant Articles if your initial output hasn't been reviewed and approved. With that said, it's highly recommended that you see to it that the initial articles you submit follow all the rules and formats as put forth by Facebook. And of course, don't forget to connect your website with your page.
To summarize things, you have to upload a logo for the new style that you created as well as for the default style. This will fix the "missing logo" problem. It worked for me so I'm hoping that it will work for you as well.