I am not an expert at all in Grenada, but I work in tech with offices all over the world and have been shipping equipment for years to our various facilities. A commercial invoice is required for most countries. There is nothing unusual with this request. Ask your vendor if they provided it in the sleeve on the outside of the box. They should have if its needed. If they didn't ask them to send you one. They will know what this is and what it means. It also appears your country may have a VAT which is why it's asking for your account. In my experience, FedEx or DHL will act as your broker and then bill you for it. If they are asking for your Tax ID number for some reason that is specific to Grenada, you'll have to give it to them.
The advice above that this has been seized is not correct. So far, they're asking for basic information. The only thing I would be worried about is why nobody else would ship it to you, and you went with some no-name company that may not have done this correctly.