Your domain will have an IPFS hash already assigned when it is created. This redirects to your ud.me profile. You will need to remove this before redirecting your domain to a Web2 domain.
To start, click manage next to your domain from the my domains page.
Now click 'Website' then click remove. You will need to sign a transaction with your wallet and wait for the transaction to go through:
If you have an existing IPFS hash you can add it to your domain: