JSON array in "body" parameter of httr::POST() - r

Question

I want to send a post request with a few variables in the body, using the httr package.
What the body would look like if it was in JSON format:
{a:"1", b:"2", c:[{d:"3", e:"4"}]}
What I tried with httr::POST()
r <- POST("http://httpbin.org/post", body = list(a = 1, b = 2, c = list(d=3, e=4)))
The error I got:
Error in curl::handle_setform(handle, .list = req$fields) :
Unsupported value type for form field 'c'.
How would I need to structure my POST() statement to send it in the format that I want mentioned above?
EDIT: On trying #renny's solution (I added verbose() for viewability) i.e. the following line
r <- POST("http://httpbin.org/post", body = json_array, encode="json", verbose())
I am able to observe that the JSON that's generated in the output is of the following format:
{"post":{"a":1,"b":2,"c":{"d":3,"e":4}}}
As you can see, the "c" variable does not have [] around it and there is a "post" variable. The following is what I want.
{"a":1,"b":2,"c":[{"d":3,"e":4}]}

Answer 1

I know it is an old question, but maybe someone will end up here like me. The problem was a missing list.
To create a json array instead of an object, list must be unnamed. So in your example:
> json_array <- list(a = 1, b = 2, c = list(list(d=3, e=4)))
> jsonlite::toJSON(json_array)
{"a":[1],"b":[2],"c":[{"d":[3],"e":[4]}]}
# auto_unbox extracts values from unnecessary arrays, not explicit lists
> jsonlite::toJSON(json_array, auto_unbox = T)
{"a":1,"b":2,"c":[{"d":3,"e":4}]}
Then you will not need to use jsonlite, since encode does the work:
httr::POST("http://httpbin.org/post", body = json_array, encode="json")
returning the response
{
"args": {},
"data": "{\"a\":1,\"b\":2,\"c\":[{\"d\":3,\"e\":4}]}",
"files": {},
"form": {},
"headers": {
"Accept": "application/json, text/xml, application/xml, */*",
"Accept-Encoding": "deflate, gzip",
"Content-Length": "33",
"Content-Type": "application/json",
...
}

Answer 2

library(httr)
json_array <- list(
post = list(a = 1, b = 2, c = list(d=3, e=4))
)
r <- POST("http://httpbin.org/post", body = json_array, encode="json")
app_data <- content(r)
Try this.
This might work out!

Answer 3

So the solution to this problem that I had to use was a JSON string in the body parameter.
If for example, the following is the JSON string under consideration:
json <- {"a":1,"b":2,"c":[{"d":3,"e":4}]}
I had to pass this JSON string as the value for the "body" parameter for httr::POST()
So the function call would look like:
r <- POST(url=url, body=json, encode="json", verbose())