There are a few hosting platforms that require a bit of additional setup. Below are the ones we know.
After a fresh install on the Byte/Hypernode platform, the Magento API is not directly accessible.
Please see the following KB article to read about how and why parts of the Magento API are not accessible by default.
https://support.hypernode.com/knowledgebase/protecting-the-magento-2-api/
When working with Hypernode it might also be that your test environment is hidden behind an additional basic authentication challenge. This will also block API communication. So if you want to connect with Commerce 365, which uses the Magento REST API, you will have to whitelist our outbound IP's.
https://support.hypernode.com/en/hypernode/nginx/basic-authentication-on-hypernode-development-plans
Check the .htaccess file that comes with your initial setup, it might be that /rest/ is blocked. Just remove that line from the files and you should be good.