Hello,
My name is Sergey. I am Freelancer from Saint Petersburg, Russia.
I can help you as an experienced WordPress programmer to fix 404 error on your multisite installation.
So, you can be able to add new sites and these new sites will be accessible properly.
2000+ successfully completed projects, including 300+ WordPress projects, speak for me. Links and reviews from my past clients available in my profile.
I am an individual, I am not a company in any meaning.
I need FTP or SSH access to start right now. And login/password into "wp-admin" Dashboard.
I can communicate via Freelancer.com.
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Sergey aka Takereal