I just went through this while trying to set up a network share for backing up Roon over my local network.
That error message doesn’t help much, does it?
I’m no expert, but I’d first suggest… did you set up a shared folder on the destination Mac? And then after you do, point to it without using the full path. (Edit: As Geoff has suggested above.)
Check out this post, where I’ve done a step-by-step to getting it done, and let me know if you have any questions or success after that.