Hi Bruno,
Thank you for reaching out to support. Please be aware that we don't support the videojs-ima plugin on this forum. For support with the plugin, you can get support from the team that maintains the plugin via their GitHub Issue Tracker. As for the error 1009 (empty VAST), there can be many reasons. Make sure your ad tag actually returns a meaningful VAST response if you open it in a browser. The error you're seeing is related to your serving. You will have to reach out to your ad provider for help modifying your serving settings. They should be able to help ensure that you get ads.
Regards,
Deepika Uragayala
IMA SDK Team