There are a variety of reasons why you may not be able to use facebook market place. To begin with, you need to be eligible with a minimum of 18 years old, and you need to reside in an area where the Marketplace is upheld. Facebook will block when your account is fresh, inactive or when it has just been used to disrupt its policies (such as commerce or community standards). Marketplace privileges may be withdrawn to accounts flagged as spam, disallowed listing or suspicious activity. Technical problems as aging apps, an issue of cache, an app glitch, VPN/location settings or incompatibility with device/browser can also wipe out access to any market place. In case access was denied, you might get a prompt to confirm your age, or request to do so using the support tools at Facebook.