These are the specifications for LNURL: https://github.com/fiatjaf/lnurl-rfc I think you're talking about a LNURL-WITHDRAW request: https://github.com/fiatjaf/lnurl-rfc/blob/luds/03.md

In any case, there is the basic problem of being offline with the Lightning Network which this post: #77191 is a good read for a potential mitigation to that problem.