To set a default image in the Configuration -> Social Meta -> Defaults area, it should be entered like:
image=https://novo.co.mz/images/novo-logo.gif
You don't need to use the full SCOpenGraph tag in that area.
The defaults area will set a fallback tag that can be used on every page of your site if no other image is specified. That means your home page will get that image, but also other pages will have it set to if no other image is set. That's usually a good thing, but just wanted to explain how the defaults work.
If you only want an image to be used on your home page, you'll need to set an Open Graph ta on that page only with the {SCOpenGraph image=...} tag. That tag can be set in a module on the page, an article that's shown on that page, or anywhere else that is shown on the home page.
I hope that helps explain, but if you need anything else, please let us know.
Thanks,
Alex