Weird behavior of POST action

[crbrox]

The postaction performs and additional level of stringification of the template so the body of the request is a string in JSON which content is the result of substitution (and the content-type is always 'application/json')
For example
with ${X} as template and X with a value of 3 it sends
"3"
as body instead of
3

or
with X is ${X} as template is sends
"X is 3"
(content-type: application/json)
instead of
X is 3

A nested level of 'serialization' that makes inappropriate for calling external APIs

[fgalan]

Fixed in PR #188