The pictures you can see on this website are minted in the Rinkeby's testnet. Rinkeby is an Ethereum test network that allows for blockchain development testing before deployment on Mainnet.
Heroku is blocking the api calls from Opensea, so you have to do these steps in order to use the website.
(If you don't do these steps, you won't see the minted NFT's in the website)
Api calls are built to this app using Cors proxies for the heroku's free web hosting. You need to request temporary access token to cors proxies in order to make API calls:
- Go to NFT-marketplace website, then open console
- In console there's error about blocked API calls (lines in red colour)
- Click the link
- Click "Request temporary access to the demo server".