Here's the spec for lnurl pay requests which is what it sounds like you're looking for: https://github.com/fiatjaf/lnurl-rfc/blob/luds/06.md

Basically you need a publicly reachable http server that

Stacker News implements this spec to provide lightning addresses for users. Because custodial wallets usually have publicly reachable http servers, they often do implement this spec so I'd check with your custodial wallet providers.