Facebook marketplace needs some structured images and documents to promote your business. You have to provide your business location, your brand, logo, product images, etc. If you don't follow the rule or you are out of range then it blocks you. If you are unable to unblock on Facebook marketplace, then you have to ensure that you confirm all the pop-up and also check there are internet connections. Also check your user's credentials. If you  still can't unblock yourself from Facebook marketplace, then you can contact Facebook customer service to get the instant results.