You cannot just take over someone else's add-on without permission. Nanocode is still active, so if it isn't compatible with 2.3, he will likely update once it gets to a state he's willing to support add-ons at.
Well I am bumping an old post, but I hope it's still relevant to you, to avoid spamming multiple posts here, I'll link to another thread where we shared links to BTCPay Server and XenForo integration, hope you find it useful (addition is free and open-source). https://xenforo.com/community/threads/bitcoin-xenforo.157683/post-1680507