If you have deployed a custom contract, you NEED to configure your royalties on OpenSea to receive royalties from secondary sales that take place on the marketplace.
Go to your Custom Contract on OpenSea (please note that OpenSea refers to contracts as collections)
Go to any NFT you have minted, click on the contract name at the top
To edit the custom contract, click on the pencil icon.
2. To set your royalties, adjust the percentage fee field (you can set a fee of up to 10%) and set your payout wallet address
3. Make sure to hit 'Submit to save your changes
Please note that royalties on OpenSea also apply to primary sales (sales by you). This means you will receive your royalties in a separate transaction.