Hey, I’m working on making LCV a payable document along with other changes, but there are many obstacles in achieving this. If you have development experience, you can find it on my branch (which has a lot more than just making LCV a payable document which might make it difficult to copy without programming experience) at GitHub - SaiFi0102/erpnext at LC-Account-Based-Purchase
I shall make a pull request from this branch maybe in a month