Migrating library to new library manager (Library not valid error)

[ScruffR]

Another user seems to have a similar issue and Particle is looking into

Publish a library

Is this your legacy repo? I’ve seen another user report a similar issue with his upload In both cases I can’t see the actual problem either. The repo already has a .cpp file in place, so I’d suppose there’s another reason.

Meanwhile you could use CLI.
There was an issue with the path seperators for Windows with 1.19.1 which got fixed in 1.19.2
Maybe there's something similar at work with Dev.