I am not sure, but i think you need DF version 2.1,
then your api should be available under :
Scripts -> Process Event Scripts -> your API ->..... your api.get.post_process.
After upgrading to 2.1 you even have to change your swagger definition.
At the beginning you need:
"swagger": "2.0",
"info": {
"title": "Your API",
"description": "xxxxxxxxxxx",
"version": "1.0.0"
},
.......