Dropdown with an array

Hi,

Don't use merge function to append two arrays. Review Appian documentation if you are not sure about that function. I am posting a sample code here, it will work for your case.

a!localVariables(
  local!reviewOptionLable1AI: {"Additional Info Required"},
  local!reviewOptionValueAI: {"AIR"},
  local!reviewOptionLabelCancel: {"Cancelled"},
  local!reviewOptionValueCancel: {"CSED"},
  local!reviewOptionLable: {local!reviewOptionLable1AI, local!reviewOptionLabelCancel},
  local!reviewOptionValue: {local!reviewOptionValueAI, local!reviewOptionValueCancel},
  a!formLayout(
    contents: {
      a!dropdownField(
        label: "Review Options",
        placeholder: "--- Select a Review Option ---",
        choiceLabels: local!reviewOptionLable,
        choiceValues: local!reviewOptionValue,
        value: "",/*your rule input*/
        saveInto: {
          /*save back to your rule input*/
        }
      )
    }
  )
)

Use the append or flatten function instead. 
Flatten is used to flat a nested array. Append, as the name suggests, is used to append a variable to an array. Using merge will create a nested array that will cause problems.