Dear @Tim Edwards I tried running simulation on your example design of

sky130_ef_ip__instramp

on ngspice. However I encounter some error messages. Could you please help me? Thank you! (I am using Harald Pretl's Docker so I changed the .lib command a little bit)

I feel like there's something missing between your 1st and 3rd screenshots. The testbench has pins "in" and "out", so there should be vectors "V(in)" and "V(out)", unless the simulation failed. But it looks like the simulation succeeded, unless there was an error message that didn't get into your screenshots. The simulation warnings in your first screenshot are not fatal and will not stop the simulation or cause an error like you're seeing in the 3rd screenshot.