Ah ok so you try to use point of sale as some kind of ecommerce shop. As Dennis said, you need to setwhole JSON of products via template parameter. This will quickly run into limitations, maybe better use a shop we have integrations to already, no need to code. https://docs.btcpayserver.org/Guide/

For deployment, easiest is docker deployment which is even more simplifyed on lunanode. https://docs.btcpayserver.org/Docker/

Alternatively use 3rd party host but has drawbacks https://docs.btcpayserver.org/Deployment/ThirdPartyHosting/