Cannot Get Field Type "Checkbox" as an argument in Custom Action

Cannot Get Field Type "Checkbox" as an argument in Custom Action

I have a custom action calling a function:
SMS.sendsms with four arguments:
- Active
- Method
- smsphone
- smsbody

In the form I have a field called "Method" that is a checkbox with two options "text" and "Email".

PROBLEM:
When craeting my New Custom Action and I select my field names for each argument, "Method" does not appear. I have tried all the argument types like int, stinr, list, etc. and "Method" does not pop-up. Is this a bug?

http://monosnap.com/image/VQIaZ8wcUpiaoZrcVnZAddrvLg5Uc0