$ add system image https://.../vyos-1.2.0-epa3-amd64.iso
...
...
What would you like to name this image? [1.2.0-epa3-]: 1.2.0-epa3
[^]
[note this extra dash]
I mean "[1.2.0-epa3-]" should be "[1.2.0-epa3]" insted