Auction Houses set their own criteria for approving bidders for their auction. While some Auction Houses approve all bidders, with minimal or no checks, other Auction Houses have more stringent requirements.
If your registration request status has been declined, this means that your bid was not processed. You need to be approved for the auction for your bid to be processed. In the future, if your registration is still pending or declined, you can reach out to the auction house to ask if they need additional information from you to approve you. You can do this by clicking on the "ASK A QUESTION" link on any of their listings.