Source path not found when generating snap image

Creating a new snap.
I have a set of binaries (executables and shared object files) that run fine on Linux (Built from c++ source files). I want to create a snap so I can install those files on a target machine and run them. I manually built a tar file and used that as the source in my snapcraft.yaml file.

When I try to generate the snap (with snapcraft --debug command), it Launches the VM and churns for a while and finally spits out:
Source path /XXXX/xxx does not exist. (This path is where I ran the snapcraft command, which contains the tar file.)
An error occurred with the instance when trying to mount with 'multipass': returned exit code 1.
Ensure that 'multipass' is setup correctly and try again.

I tried to create a new part to reference the folder. Same error.
The folder certainly does exist on the local machine, I assume this refers to the VM. How do I force the folder to be created?