This is possibly because of your network connection. If you using a VPN/office laptop/anonymized networks/a dedicated home network, disconnect from it or try from another network. Requests from such connections are considered as bots and reject the access. It is implemented on purpose because there are a lot of bad users scraping the site for slots info without contributing..

Give it a try on your mobile network (not Wi-Fi) to verify it it's the issue with the network.