Data availability differs between collections. Some collections only acquire imagery when tasked to do so (Planet Skysat and Maxar WorldView), and so your location will have an image only, if someone previously tasked a satellite to capture it. Sentinel Hub offers full data archive to users, but tasking is not yet supported. Planet PlanetScope, on the other hand, captures the whole globe systematically every day.
It is thus possible that no image is available for your polygon at the time of your interest, or that the available image is cloudy. Or, your location could have hundreds of quality images.
It’s best to check for data availability in EO Browser, where you can search archive data and see low resolution previews of products. This is best done before you purchase commercial quota, as we can’t offer refunds. Searching is available to all users with a paid Sentinel Hub subscription, and no API key is needed, so you can check if data you need is there beforehand.
See how to search and order commercial data in EO Browser and Requests Builder.