Trying to show a hidden field in a subform but get "invalid task in subfrom action.

Trying to show a hidden field in a subform but get "invalid task in subfrom action.

When trying to show a hidden field in a subform but get "invalid task in subfrom action" when trying to save the action. The script is below. I look forward to your help.

if(input.Jobs.Job_Type = "Warranty")
 {
show Jobs.Warranty_Parts_Cost;
 }