Have you tried the fix mentioned here?
If that fixed it, the issue would likely be a version mismatch between nest and the versioned release of pijul, in my admittedly limited understanding of the problem; nest’s source code is not public (see pijul/pijul - Discussion #963 - Thrussh should be updated to fix push command for nest)
As for contributing, being new (this is my first interaction with people using pijul in fact, hi!), I can’t comment on how to contribute, I feel like the manual book wants to make me believe that the repo’s discussion section is the place for this to happen, but far as I can tell while it does get some talks going, it seems incredibly stale in the case of pijul/pijul itself, the above issue is merely a version bump, has been known since February, and still hasn’t been merged