Is your developer requesting FTP Access?
Please copy and paste the instructions below to use with your developer.
Your blog is hosted on a secure controlled managed WordPress hosting platform. We are not able to provide any FTP or SSH. Your developer can do all CSS changes via the Custom CSS editor and anything above that the developer would need to provide you the theme and any required plugins in zip format.
You would then send those .zip files to us via email@example.com where they will be reviewed within about 24 hours.
As long as they follow the WordPress Codex best practices, are secure and use proper PHP and don’t make abusive database calls, they will be approved and then activated on your blog.