Your website, most probably, is either not published or under maintenance mode. Note that 10Web Manager can only connect to already live websites. You’ll have to install plugins manually using the WP directory (or upload .zip file) until your site is published and connected.
It may also be useful to:
1. Check if WordPress REST API works by going to https://WEBSITE_URL/?rest_route=/
If you see JSON output (bunch of text on a white page) without error messages, it works! REST API may be blocked by some security plugins or by hosting providers.
2. Check file system permissions. If 10Web Manager plugin doesn’t have permissions, you’ll see the error message “10Web Manager plugin does not have file system permissions to install, update and delete products. You can download your purchased plugins here. In order to fix permission issue, please contact our customer care team”.